Recent progress in thick‐film organic photovoltaic devices: Materials, devices, and processing - Zhang, Difei; Fan, Baobing; Ying, Lei; Li, Ning; Brabec, Christoph; Huang, Fei; Cao, Yonghai (SusMat, 2021)
A successful transfer of organic photovoltaic technologies from lab to fab has to overcome a range of critical challenges such as developing high-mobility light-harvesting materials, minimizing the upscaling losses, designing advanced solar modules, controlling film quality, decreasing overall cost, and extending long-operation lifetime. To realize large-area devices toward practical applications, much effort has been devoted to understanding the fundamental mechanism of how molecular structures, device architectures, interfacial engineering, and light management and carrier dynamics affect photovoltaic performance. Such studies addressed various fundamental issues of charge carrier behavior in organic heterojunctions primarily in terms of exciton generation dependence upon light incidence, charge transportation dependence on built-in electric field, and charge extraction versus recombination. In consideration of high-throughput roll-to-roll process for large-scale fabrication of organic photovoltaic devices, it is highly appreciable to realize high power conversion efficiencies that are highly tolerable to the film thickness. Herein we summarize the recent progress in developing thick-film organic photovoltaic devices from the perspective of efficiency-loss mechanisms, material design, and device optimization strategies, proposing guidelines for designing high-efficiency thickness-insensitive devices toward mass production.

Recombination dynamics as a key determinant of open circuit voltage in organic bulk heterojunction solar cells: A comparison of four different donor polymers - Maurano, Andrea; Hamilton, Rick; Shuttle, Chris G.; Ballantyne, Amy M.; Nelson, Jenny; O'Regan, Brian; Zhang, Weimin; Mcculloch, Iain; Azimi, Hamed; Morana, Mauro; Brabec, Christoph; Durrant, James R. (Advanced Materials, 2010)
Transient photovoltage and charge extraction analyses are employed to analyzes charge carrier densities and bimolecular recombination dynamics in organic polymer: fullerene solar cells under open circuit operating conditions, employing four different donor polymers. An equation is derived which allows us to calculate the device V from these kinetic measurements. This equation allows us to calculate voltage output of devices within ± 25 meV of directly measured values. This analysis thus allows us to relate device open circuit voltage directly to the kinetics of bimolecular recombination, and thereby the influence of nanomorphology upon device voltage output. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: bimolecular recombination; charge dynamics; open circuit voltage; organic solar cell; power conversion efficiency

Red-emitting Ca 1-xSr xS:Eu 2+ phosphors as light converters for plant-growth applications - Xia, Qi; Batentschuk, Miroslaw; Osvet, Andres; Richter, Peter; Häder, Donat-Peter; Schneider, Jürgen; Wondraczek, Lothar; Winnacker, Albrecht; Brabec, Christoph (2011 MRS Spring Meeting, 2012)
A series of Ca Sr S:Eu phosphors were synthesized with solid state reactions and with various Ca/Sr ratio and Eu doping concentrations. The influences of the lattice composition and the Eu doping level on photoluminescent properties were analyzed. With doping concentrations between 0.1 to 3 mol%, concentration quenching takes place leading to the decrease of luminance; the emission maxima are also red-shifted. Further, this work reports enhanced photosynthetic activities of intact spinach leaves due to spectral modification of simulated solar irradiation by one synthesized phosphor (Ca Sr S:Eu ). The CO assimilation rates of intact spinach leaves were monitored with an effective homemade photosynthesis measurement system with controlled light conditions. The phosphor could efficiently convert the photosynthetically less active green part of the solar spectrum into the red, with a broad-band red emission centered at 650 nm and a halfband-width of 68 nm, giving an excellent match with the absorption spectrum of spinach chloroplasts. By careful referencing the photon flux, we found an enhanced photosynthetic activities by about 30% due to the emission of the phosphor. © 2011 Materials Research Society.
Keywords: Assimilation rate; Broad bands; Concentration quenching; Doping concentration; Doping levels; Emission maxima; Light conditions; Measurement system; Photo-luminescent properties; Photon flux; Photosynthetic activity; Red emissions; Red-shifted; Solar irradiation; Solar spectrum; Spectral modifications; Spinach leaves Engineering controlled terms: Calcium; Carbon dioxide; Light emission; Phosphors; Solar radiation; Solid state reactions Engineering main heading: Europium

Reduced voltage losses yield 10% efficient fullerene free organic solar cells with >1 V open circuit voltages - Baran, D.; Kirchartz, T.; Wheeler, S.; Dimitrov, S.; Abdelsamie, M.; Gorman, J.; Ashraf, R. S.; Holliday, S.; Wadsworth, A.; Gasparini, Nicola; Kaienburg, P.; Yan, H.; et al. (Energy and Environmental Science, 2016)
Optimization of the energy levels at the donor-acceptor interface of organic solar cells has driven their efficiencies to above 10%. However, further improvements towards efficiencies comparable with inorganic solar cells remain challenging because of high recombination losses, which empirically limit the open-circuit voltage (V) to typically less than 1 V. Here we show that this empirical limit can be overcome using non-fullerene acceptors blended with the low band gap polymer PffBT4T-2DT leading to efficiencies approaching 10% (9.95%). We achieve V up to 1.12 V, which corresponds to a loss of only E/q - V = 0.5 ± 0.01 V between the optical bandgap E of the polymer and V. This high V is shown to be associated with the achievement of remarkably low non-geminate and non-radiative recombination losses in these devices. Suppression of non-radiative recombination implies high external electroluminescence quantum efficiencies which are orders of magnitude higher than those of equivalent devices employing fullerene acceptors. Using the balance between reduced recombination losses and good photocurrent generation efficiencies achieved experimentally as a baseline for simulations of the efficiency potential of organic solar cells, we estimate that efficiencies of up to 20% are achievable if band gaps and fill factors are further optimized.
Keywords: Engineering controlled terms: Energy gap; Fullerenes; Open circuit voltage; Organic solar cells; Polymer solar cells; Timing circuits Donor-acceptor interfaces; Fullerene free; Inorganic solar cells; Low bandgap polymers; Non-radiative recombinations; Orders of magnitude; Photocurrent generations; Recombination loss Engineering main heading: Solar cells

Reducing burn-in voltage loss in polymer solar cells by increasing the polymer crystallinity - Heumueller, Thomas; Mateker, William R.; Sachs-Quintana, I. T.; Vandewal, Koen; Bartelt, Jonathan A.; Burke, Timothy M.; Ameri, Tayebeh; Brabec, Christoph; Mcgehee, Michael D. (Energy and Environmental Science, 2014)
In order to commercialize polymer solar cells, the fast initial performance losses present in many high efficiency materials will have to be managed. This burn-in degradation is caused by light-induced traps and its characteristics depend on which polymer is used. We show that the light-induced traps are in the bulk of the active layer and we find a direct correlation between their presence and the open-circuit voltage loss in devices made with amorphous polymers. Solar cells made with crystalline polymers do not show characteristic open circuit voltage losses, even though light-induced traps are also present in these devices. This indicates that crystalline materials are more resistant against the influence of traps on device performance. Recent work on crystalline materials has shown there is an energetic driving force for charge carriers to leave amorphous, mixed regions of bulk heterojunctions, and charges are dominantly transported in pure, ordered phases. This energetic landscape allows efficient charge generation as well as extraction and also may benefit the stability against light-induced traps. This journal is © the Partner Organisations 2014.
Keywords: Engineering controlled terms: Crystalline materials; Heterojunctions; Open circuit voltage; Solar cells Amorphous polymers; Bulk heterojunction; Charge generation; Crystalline polymers; Device performance; Open circuit voltage loss; Polymer crystallinity; Polymer Solar Cells Engineering main heading: Polymers GEOBASE Subject Index: crystallinity; energy efficiency; photovoltaic system; polymer; solar power

Reducing charge trapping in PbS colloidal quantum dot solids - Balazs, D. M.; Nugraha, M. I.; Bisri, S. Z.; Sytnyk, M.; Heiß, Wolfgang; Loi, M. A. (Applied Physics Letters, 2014)
Understanding and improving charge transport in colloidal quantum dot solids is crucial for the development of efficient solar cells based on these materials. In this paper, we report high performance field-effect transistors based on lead-sulfide colloidal quantum dots (PbS CQDs) crosslinked with 3-mercaptopropionic acid (MPA). Electron mobility up to 0.03 cm(2)/Vs and on/off ratio above 10(5) was measured; the later value is the highest in the literature for CQD Field effect transistors with silicon-oxide gating. This was achieved by using high quality material and preventing trap generation during fabrication and measurement. We show that air exposure has a reversible p-type doping effect on the devices, and that intrinsically MPA is an n-type dopant for PbS CQDs. (C) 2014 AIP Publishing LLC.
Keywords: 3-mercaptopropionic acid; Colloidal quantum dots; High-quality materials; N-type dopants; On/off ratio; P-type doping; Pbs colloidal quantum dots; Trap generation

Reducing energy barrier of δ-to-α phase transition for printed formamidinium lead iodide photovoltaic devices - Xu, Zhenhua; Zeng, Linxiang; Hu, Jinlong; Wang, Zhen; Zhang, Putao; Brabec, Christoph; Forberich, Karen; Mai, Yaohua; Guo, Fei (Nano Energy, 2022)
Recent progress in perovskite photovoltaics has witnessed a growing interest in formamidinium lead iodide (FAPbI3), primarily due to its high efficiency potential and excellent stability. However, the high energy barrier of δ-to-α phase transition presents a major hurdle to fabricate phase-pure α-FAPbI3 layers. Here, we report a two-step phase transition process to deposit high-quality photovoltaic α-FAPbI3 films by printing method. This is realized by judicious selection of a Lewis base N-methyl-2-pyrrolidone (NMP) and its counter Lewis acid, which enables the regulation of intermediary phase to reduce the energy barrier. With fine tuning the phase transition pathway, phase-pure and stable α-FAPbI3 perovskite films are obtained, which yield solar devices with a champion efficiency of 21.35%. The printed mini-modules with active areas of 12.32 cm2 and 55.44 cm2 are also fabricated, giving efficiencies of 17.07% and 14.17%, respectively. This work provides new insights of α-FAPbI3 crystallization for constructing efficient and stable printed photovoltaic devices.
CRIS-Team Scopus Importer:2021-11-12
Keywords: Energy barrier tuning; Mini-modules; Printed α-FAPbI; Two-step crystallization

Reducing Open-Circuit Voltage Losses in All-Inorganic Perovskite Cells by Dedoping - Peng, Zijian; Tian, Jingjing; Zhang, Kaicheng; These, Albert; Xie, Zhiqiang; Zhao, Yicheng; Osvet, Andres; Guo, Fei; Lüer, Larry; Li, Ning; Brabec, Christoph (ACS Energy Letters, 2023)
CsPbI2Br is an attractive photovoltaic material due to its promising optoelectronic properties. However, the corresponding perovskite solar cells (PSCs) with p-i-n configuration suffer from low open-circuit voltage (VOC) and fill factor (FF), limiting their application in tandem solar cells. Here, we propose using the fullerene ICBA as the electron charge transporting layer (ETL), forming a better interfacial contact and enhancing the internal quasi-Fermi level splitting (QFLS). A further reduction of VOC losses of around 0.1 V was achieved by an ultrathin phenethylammonium chloride (PEACl) layer between the perovskite and the ETL. We precisely study the VOC improvement and find that passivation of surface recombination contributes only 20 mV, while more importantly, a major increase of 80 mV is achieved by dedoping the perovskite surface, which removes a non-negligible electron extraction barrier. Our results give helpful direction regarding how to further improve VOC in p-i-n perovskite cells.
CRIS-Team Scopus Importer:2023-04-21

Reducing the efficiency–stability–cost gap of organic photovoltaics with highly efficient and stable small molecule acceptor ternary solar cells - Baran, Derya; Ashraf, Raja Shahid; Hanifi, David A.; Abdelsamie, Maged; Gasparini, Nicola; Röhr, Jason A.; Holliday, Sarah; Wadsworth, Andrew; Lockett, Sarah; Neophytou, Marios; Emmott, Christopher J M; Nelson, Jenny; et al. (Nature Materials, 2016)
Technological deployment of organic photovoltaic modules requires improvements in device light-conversion efficiency and stability while keeping material costs low. Here we demonstrate highly efficient and stable solar cells using a ternary approach, wherein two non-fullerene acceptors are combined with both a scalable and affordable donor polymer, poly(3-hexylthiophene) (P3HT), and a high-efficiency, low-bandgap polymer in a single-layer bulk-heterojunction device. The addition of a strongly absorbing small molecule acceptor into a P3HT-based non-fullerene blend increases the device efficiency up to 7.7 ± 0.1% without any solvent additives. The improvement is assigned to changes in microstructure that reduce charge recombination and increase the photovoltage, and to improved light harvesting across the visible region. The stability of P3HT-based devices in ambient conditions is also significantly improved relative to polymer:fullerene devices. Combined with a low-bandgap donor polymer (PBDTTT-EFT, also known as PCE10), the two mixed acceptors also lead to solar cells with 11.0 ± 0.4% efficiency and a high open-circuit voltage of 1.03 ± 0.01 V.
Keywords: Engineering controlled terms: Efficiency; Energy gap; Fullerenes; Heterojunctions; Molecules; Open circuit voltage; Photovoltaic cells; Polymer solar cells; Polymers; Solar power generation Ambient conditions; Bulk-heterojunction devices; Charge recombinations; Device efficiency; Low bandgap polymers; Organic photovoltaics; Poly-3-hexylthiophene; Solvent additives Engineering main heading: Solar cells

Reducing Voltage Losses in Organic Photovoltaics Requires Interfacial Disorder Management - Wang, Rong; Han, Leng; Li, Ning; Chochos, Christos L.; Gregoriou, Vasilis G.; Lüer, Larry; Brabec, Christoph (Advanced Energy Materials, 2024)
Thanks to the introduction of non-fullerene acceptors, efficiencies of organic photovoltaics are now approaching 20%. Closing the gap with inorganic photovoltaics requires minimizing voltage losses without penalizing charge extraction, for which microstructure control is crucial. However, the complex interplay between microstructure and charge generation, recombination, and extraction has so far not been unraveled. Here, a systematic study linking device performance to distinct microstructural features via machine learning is presented. Building bi-layer devices allows to separately study the influence of aggregation and disorder on the energies and lifetimes of bulk and interfacial states. Unambiguous assignments of specific structural motifs to the device photophysics are thus possible. It is found that the control of aggregation-caused quenching is decisive for the exciton splitting efficiency and thus the carrier generation. Furthermore, the static disorder at the donor–acceptor interface controls the nonradiative recombination by shifting the excited state population from the bulk toward the interface. Finally, the amount of disorder in the bulk is found decisive for charge extraction. The finding that charge generation, recombination, and extraction are controlled by distinct structural features, is the key to optimizing these motifs independently, which will pave the way for organic photovoltaics toward the detailed balance limit.
CRIS-Team Scopus Importer:2024-05-03
Keywords: interfacial energy states; machine learning; microstructure; organic solar cells; voltage loss

Reduktion von Metallartefakten durch multipositionale Datenfusion in der industriellen Röntgen-Computertomographie - Herl, Gabriel; Hiller, Jochen; Kasperl, Stefan; Maier, Andreas (Technisches Messen, 2019)
Zusammenfassung Metallartefakte stellen eine große Herausforderung für das Messen mit Röntgen-Computertomographie dar. Dieser Beitrag stellt die Methode der multipositionalen Datenfusion zur Reduktion von Metallartefakten vor. Dazu werden mehrere Scans desselben Objekts bei unterschiedlicher Objekt-positionierung durchgeführt, aufeinander registriert und zur Fusion gemeinsam unter Betrachtung eines lokalen Gütemaßes rekonstruiert. In praxisnahen Experimenten wird der Mehrwert der Methode gezeigt. Insbesondere wird dargestellt, wie mit wenig Aufwand und ohne Vorwissen Kunststoffstrukturen trotz starker Metallartefakte sichtbar gemacht werden können, womit das Verfahren ein Alleinstellungsmerkmal gegenüber den existierenden Metallartefaktreduktionsverfahren aufweist. Abstract Metal artifacts represent a major challenge for measuring with X-ray computed tomography. This paper presents a method for multipositional data fusion for the reduction of metal artifacts. For this purpose, several scans of the same object are performed with different object positioning, registered on each other and then reconstructed together using a local quality measure. The added value of the method is demonstrated in practical experiments. In particular, it is shown how plastic structures can be made visible despite strong metal artifacts with little effort and without prior knowledge, giving the method a unique selling point compared to existing metal artefact reduction methods.
Keywords: X-ray computed tomography; CT; metal artifact reduction; multipositional data fusion

Regulating the Surface Passivation and Residual Strain in Pure Tin Perovskite Films - Hu, Manman; Nie, Riming; Kim, Hyeonwoo; Wu, Jianchang; Chen, Shanshan; Park, Byung-Wook; Kim, Gwisu; Kwon, Hyoung-Woo; Seok, Sang Il (ACS Energy Letters, 2021)
The passivation of electronic defects at the surfaces and grain boundaries of perovskite materials is one of the most important strategies for suppressing charge recombination in perovskite solar cells (PSCs). Although several passivation molecules have been investigated, few studies have focused on their application in regulating both the surface passivation and residual strain of perovskite films. In this study, the residual strain distribution profiles of the Cs0.1FA0.9SnI3 perovskite thin films and their effect on the photovoltaic device efficiencies were investigated. We found a gradient distribution of the out-of-plane compressive strain that correlated with the compositional inhomogeneity perpendicular to the substrate surface. By deliberately engineering dual effects of the surface passivation and residual strain, we achieved a record power conversion efficiency of up to 9.06%, the highest ever reported in a typical n-i-p architecture.
CRIS-Team Scopus Importer:2021-11-05

Relation of Nanostructure and Recombination Dynamics in a Low-Temperature Solution-Processed CuInS2 Nanocrystalline Solar Cell - Azimi, Seyed Hamed; Heumüller, Thomas; Gerl, Andreas; Matt, Gebhard; Kubis, Peter; Distaso, Monica; Ahmad, Rameez; Akdas, Tugce; Richter, Moses; Peukert, Wolfgang; Brabec, Christoph (Advanced Energy Materials, 2013)
The understanding and control of nanostructures with regard to transport and recombination mechanisms is of key importance in the optimization of the power conversion efficiency (PCE) of solar cells based on inorganic nanocrystals. Here, the transport properties of solution-processed solar cells are investigated using photo-CELIV (photogenerated charge carrier extraction by linearly increasing voltage) and transient photovoltage techniques; the solar cells are prepared by an in-situ formation of CuInS2 nanocrystals (CIS NCs) at the low temperature of 270 °C. Structural and morphological analyses reveal the presence of a metastable CuIn5S8 phase and a disordered morphology in the CuInS2 nanocrytalline films consisting of polycrystalline grains at the nanoscale range. Consistent with the disordered morphology of the CIS NC thin films, the CIS NC devices are characterized by a low carrier mobility. The carrier density dynamic indicates that the recombination kinetics in these devices follows the dispersive bimolecular recombination model and does not fully behave in a diffusion-controlled manner, as expected by Langevin-type recombination. The mobility–lifetime product of the charge carriers properly explains the performance of the thin (200 nm) CIS NC solar cell with a high fill-factor of 64% and a PCE of over 3.5\
Keywords: nanostructures; power; conversion; nanocrystal

Reliability of charge carrier recombination data determined with charge extraction methods - Kniepert, Juliane; Paulke, Andreas; Perdigón-Toro, Lorena; Kurpiers, Jona; Zhang, Huotian; Gao, Feng; Yuan, Jun; Zou, Yingping; Le Corre, Vincent Marc; Koster, L Jan Anton; Neher, Dieter (Journal of Applied Physics, 2019)
Charge extraction methods are popular for measuring the charge carrier density in thin film organic solar cells and to draw conclusions about the order and coefficient of nongeminate charge recombination. However, results from such studies may be falsified by inhomogeneous steady state carrier profiles or surface recombination. Here, we present a detailed drift-diffusion study of two charge extraction methods, bias-assisted charge extraction (BACE) and time-delayed collection field (TDCF). Simulations are performed over a wide range of the relevant parameters. Our simulations reveal that both charge extraction methods provide reliable information about the recombination order and coefficient if the measurements are performed under appropriate conditions. However, results from BACE measurements may be easily affected by surface recombination, in particular for small active layer thicknesses and low illumination densities. TDCF, on the other hand, is more robust against surface recombination due to its transient nature but also because it allows for a homogeneous high carrier density to be inserted into the active layer. Therefore, TDCF is capable to provide meaningful information on the order and coefficient of recombination even if the model conditions are not exactly fulfilled. We demonstrate this for an only 100 nm thick layer of a highly efficient nonfullerene acceptor (NFA) blend, comprising the donor polymer PM6 and the NFA Y6. TDCF measurements were performed as a function of delay time for different laser fluences and bias conditions. The full set of data could be consistently fitted by a strict second order recombination process, with a bias- and fluence-independent bimolecular recombination coefficient k(2) = 1.7 x 10(-17)m(3) s(-1). BACE measurements performed on the very same layer yielded the identical result, despite the very different excitation conditions. This proves that recombination in this blend is mostly through processes in the bulk and that surface recombination is of minor importance despite the small active layer thickness. Published under license by AIP Publishing.

Reliability of IR-imaging of PV-plants under operating conditions - Buerhop, Cl; Schlegel, D.; Niess, M.; Vodermayer, C.; Weigmann, R.; Brabec, Christoph (Solar Energy Materials and Solar Cells, 2012)
The quality check of PV-plants under certain operating conditions by employing infrared-imaging has acquired significance during the last years. In order to prove the reliability of these techniques in terms of power loss, life time, critical temperatures and failure mechanisms, fifteen PV-plants were investigated in detail. In total, about 260 dismantled modules were analyzed by power measurements as well as electroluminescence and IR-thermography. Apart from revealing the reliability of this technique, the evaluated data manifest various failure mechanisms, like cell fracture, deficient solder joints, short-circuited cells and bypassed substrings. The impact of these frequently detected defects on the resulting temperature, the IV-curve and the power output is discussed. Finally, differing defects can be diagnosed by characteristic temperature differences. In conclusion, the reliability and usefulness of infrared-mapping of PV-plants were proved with the result, that all modules having cells with increased temperature show remarkably reduced power output. (C) 2012 Elsevier B.V. All rights reserved.
Keywords: IR-imaging; Outdoor testing; Reliability; Operating conditions; Electroluminescence

Reliable comparison of perovskite solar cell performance using maximum power point tracking - Rakocevic, Lucija; Ernst, Felix; Gehlhaar, Robert; Aernouts, Tom; Brabec, Christoph; Poortmans, Jef (International Conference on Hybrid and Organic Photovoltaics, 2019)
Organometallic halide based thin film PV has achieved research device efficiencies of 23.7 %, surpassing other thin film PV technologies in less than a decade of research. However, hysteretic behavior caused by ion movement in perovskite semiconductor affecting charge carrier extraction can inhibit a reliable performance measurement. This behavior, reflected in transient current variations following voltage alteration, can be dependent on preconditioning of the sample, scan rate, temperature and the composition of the perovskite solar cell stack itself. Therefore, a reliable performance comparison of perovskite solar cells is non-trivial. We examine the robustness of maximum power point tracking (MPPT) using three measurement algorithms to compare the performance of three n-i-p planar perovskite stacks. Moreover, we extract the relevant measurement parameters for a reliable MPPT. Figure shows how the measurement delay affects the measured performance of a solar cell for each of the studied algorithms. As the result of the study, we propose a measurement protocol to determine the device PCE applicable in everyday laboratory testing of perovskite solar cells. Finally, we draw attention to the importance of defining a robust and universal measurement procedure for comparison of various perovskite based thin film PV devices researched in the community<br

Reliable Performance Comparison of Perovskite Solar Cells Using Optimized Maximum Power Point Tracking - Rakocevic, Lucija; Ernst, Felix; Yimga, Nadine T.; Vashishtha, Saumye; Aernouts, Tom; Heumüller, Thomas; Brabec, Christoph; Gehlhaar, Robert; Poortmans, Jef (Solar RRL, 2019)
Performance comparison of perovskite solar cells with different architectures is nontrivial. J-V sweeps can be unreliable due to stack-dependent output variations affected by sample preconditioning, scan rate, scan direction, and temperature. Maximum power point tracking is regarded as a more reliable performance measurement. In this study, a two-step measuring procedure is proposed for quick and unbiased comparison of perovskite-based solar cells. In the proposed procedure, the transient current density characterization step is used to determine optimal parameters for maximum power point tracking performance characterization. Moreover, factors affecting time limited maximum power point tracking by comparing performance and output of three different maximum power point tracking algorithms applied to devices, from three planar n-i-p perovskite stacks, are analyzed and identified. Numerical simulation is used to model differences and define limitations of the algorithms. As a result, it is shown that measurement delay and voltage step can have a crucial effect on maximum power point tracking output, regardless of the chosen algorithm.
CRIS-Team WoS Importer:2019-03-08

Renewed Prospects for Organic Photovoltaics - Zhang, Guichuan; Lin, Francis R.; Qi, Feng; Heumüller, Thomas; Distler, Andreas; Egelhaaf, Hans-Joachim; Li, Ning; Chow, Philip C. Y.; Brabec, Christoph; Jen, Alex K. -Y.; Yip, Hin-Lap (Chemical Reviews, 2022)
Organic photovoltaics (OPVs) have progressed steadily through three stages of photoactive materials development: (i) use of poly(3-hexylthiophene) and fullerene-based acceptors (FAs) for optimizing bulk heterojunctions; (ii) development of new donors to better match with FAs; (iii) development of non-fullerene acceptors (NFAs). The development and application of NFAs with an A-D-A configuration (where A = acceptor and D = donor) has enabled devices to have efficient charge generation and small energy losses (Eloss < 0.6 eV), resulting in substantially higher power conversion efficiencies (PCEs) than FA-based devices. The discovery of Y6-type acceptors (Y6 = 2,2'-((2Z,2'Z)-((12,13-bis (2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]-thiadiazolo [3,4-e]-thieno- [2 ",3 ":4',5']thieno-[2',3':4,5]pyrrolo-[3,2-g]thieno-[2',3':4,5]thieno-[3,2-b]indole-2,10- diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))-dimalononitrile) with an A-DA' D-A configuration has further propelled the PCEs to go beyond 15% due to smaller Eloss values (& SIM;0.5 eV) and higher external quantum efficiencies. Subsequently, the PCEs of Y6-series single-junction devices have increased to > 19% and may soon approach 20%. This review provides an update of recent progress of OPV in the following aspects: developments of novel NFAs and donors, understanding of the structure-property relationships and underlying mechanisms of state-of-the-art OPVs, and tasks underpinning the commercialization of OPVs, such as device stability, module development, potential applications, and high-throughput manufacturing. Finally, an outlook and prospects section summarizes the remaining challenges for the further development of OPV technology.
CRIS-Team WoS Importer:2022-08-26

Representative identification of spectra and environments (RISE) using k-means - Looney, Erin E.; Liu, Zhe; Classen, Andrej; Liu, Haohui; Riedel, Nicholas; Braga, Marília; Balaji, Pradeep; Augusto, André; Buonassisi, Tonio; Marius Peters, Ian (Progress in Photovoltaics, 2020)
Spectral differences affect solar cell performance, an effect that is especially visible when comparing different solar cell technologies. To reproduce the impact of varying spectra on solar cell performance in the lab, a unique classification of spectra is needed, which is currently missing in literature. The most commonly used classification, average photon energy (APE), is not unique, and a single APE value may represent various spectra depending on location. In this work, we propose a classification method based on an iterative use of the k-means clustering algorithm. We call this method RISE (Representative Identification of Spectra and the Environment). We define a set of 18 spectra using RISE and reproduce the spectral impact on energy yield for various solar cell technologies and locations. We explore effects on yield for commercially available solar cell technologies (Si and CdTe) in four locations: Singapore (fully humid equatorial climate), Colorado (cold arid), Brazil (warm, humid, and subtropical), and Denmark (fully humid warm temperature). We then reduce our findings to practice by implementing the spectrum set into an LED current–voltage (IV) tester. We verify our performance predictions using our set of representative spectra to reproduce energy yield differences between Si solar cells and CdTe solar cells with an average error of less than 1.5 ± 0.5% as compared to over 5% when using standard testing conditions.
CRIS-Team Scopus Importer:2020-12-18
Keywords: energy yield; machine learning; photovoltaics; solar spectra classification

Resolving a Critical Instability in Perovskite Solar Cells by Designing a Scalable and Printable Carbon Based Electrode-Interface Architecture - Mashhoun, Sara; Hou, Yi; Chen, Haiwei; Tajabadi, Fariba; Taghavinia, Nima; Egelhaaf, Hans-Joachim; Brabec, Christoph (Advanced Energy Materials, 2018)
Thin-film solar cells based on hybrid organo-halide lead perovskites achieve over 22% power conversion efficiency (PCE). A photovoltaic technology at such high performance is no longer limited by efficiency. Instead, lifetime and reliability become the decisive criteria for commercialization. This requires a standardized and scalable architecture which does fulfill all requirements for larger area solution processing. One of the most highly demanded technologies is a low temperature and printable conductive ink to substitute evaporated metal electrodes for the top contact. Importantly, that electrode technology must have higher environmental stability than, for instance, an evaporated silver (Ag) electrode. Herein, planar and entirely low-temperature-processed perovskite devices with a printed carbon top electrode are demonstrated. The carbon electrode shows superior photostability compared to reference devices with an evaporated Ag top electrode. As hole transport material, poly (3′hexyl thiophene) (P3HT) and copper(I) thiocyanate (CuSCN), two cost-effective and commercially available p-type semiconductors are identified to effectively replace the costlier 2,2′,7,7′-Tetrakis-(N,N-di-4-methoxyphenylamino)- 9,9′-spirobifluorene (spiro-MeOTAD). While methylammonium lead iodide (MAPbI3)-based perovskite solar cells (PSCs) with an evaporated Ag electrode degrade within 100 h under simulated sunlight (AM 1.5), fully solution-processed PSCs with printed carbon electrodes preserve more than 80% of their initial PCE after 1000 h of constant illumination.<br
Keywords: carbon electrodes; hole transporting material; stability; perovskite solar cells; photovoltaic devices

Response to Comment on "Charge Carrier Extraction in Organic Solar Cells Governed by Steady-State Mobilities" - Le Corre, Vincent Marc; Rahimi Chatri, Azadeh; Doumon, Nutifafa Y.; Koster, L Jan Anton (Advanced Energy Materials, 2018)

Results of SIMS, LTPL and temperature-dependent Hall effect measurements performed on Al-doped alpha-SiC substrates grown by the M-PVT method - Contreras, Sylvie; Zielinski, Marcin; Konczewicz, Leszek; Blanc, Caroline; Juillaguet, Sandrine; Müller, Ralf; Künecke, Ulrike; Wellmann, Peter; Camassel, J. (Materials Science Forum, 2006)
We report on investigation of p-type doped, SiC wafers grown by the Modified-Physical Vapor Transport (M-PVT) method. SIMS measurements give Al concentrations in the range 10(18) to 10(20) cm(-3), with weak Ti concentration but large N compensation. To measure the wafers' resistivity, carrier concentration and mobility, temperature-dependant Hall effect measurements have been made in the range 100-850 K using the Van der Pauw method. The temperature dependence of the mobility suggests higher Al concentration, and higher compensation, than estimated from SIMS. Additional LTPL measurements show no evidence of additional impurities in the range of investigation, but suggest that the additional compensation may come from an increased concentration of non-radiative centers.
Keywords: p-type bulk; Al doping; Hall effect; SIMS

Revealing Charge Carrier Mobility and Defect Densities in Metal Halide Perovskites via Space-Charge-Limited Current Measurements - Le Corre, Vincent Marc; Duijnstee, Elisabeth A; El Tambouli, Omar; Ball, James M; Snaith, Henry J.; Lim, Jongchul; Koster, L Jan Anton (ACS Energy Letters, 2021)
Space-charge-limited current (SCLC) measurements have been widely used to study the charge carrier mobility and trap density in semiconductors. However, their applicability to metal halide perovskites is not straightforward, due to the mixed ionic and electronic nature of these materials. Here, we discuss the pitfalls of SCLC for perovskite semiconductors, and especially the effect of mobile ions. We show, using driftdiffusion (DD) simulations, that the ions strongly affect the measurement and that the usual analysis and interpretation of SCLC need to be refined. We highlight that the trap density and mobility cannot be directly quantified using classical methods. We discuss the advantages of pulsed SCLC for obtaining reliable data with minimal influence of the ionic motion. We then show that fitting the pulsed SCLC with DD modeling is a reliable method for extracting mobility, trap, and ion densities simultaneously. As a proof of concept, we obtain a trap density of 1.3 x 10(13) cm(-3), an ion density of 1.1 x 10(13) cm(-3), and a mobility of 13 cm(2) V-1 s(-1) for a MAPbBr(3) single crystal.

Revealing Degradation Mechanisms in 3D/2D Perovskite Solar Cells under Photothermal Accelerated Ageing - Peng, Zijian; Vincze, Andrej; Streller, Fabian; Le Corre, Vincent Marc; Zhang, Kaicheng; Li, Chaohui; Tian, Jingjing; Liu, Chao; Luo, Junsheng; Zhao, Yicheng; Späth, Andreas; Fink, Rainer; et al. (Energy and Environmental Science, 2024)
Three-dimensional/two-dimensional (3D/2D) heterojunctions in perovskite solar cells exhibit excellent optoelectronic properties and enhanced stability under mild ageing conditions. However, their performance degrades drastically under harsh ageing conditions. This study reveals the intrinsic instability of mono-ammonium based 2D perovskites (2D-mono) under photo-thermal ageing, which decompose into PbI2 and metallic lead (Pb0). The structural collapse promotes vacancy formation and facilitates iodide migration to the anode. As a result, it triggers a redox reaction that reduces the transport layer’s mobility and doping concentration, leading to a significant increase in series resistance. Compared to mono-ammonium-2D structure, di-ammonium-2D (2D-di) based interfaces demonstrate superior structural stability and effectively block iodide migration into the transporting layer. However, blocking-induced uneven iodide distribution leads to interstitial defect formation in the 3D layer, exacerbating non-radiative recombination. To address it, we propose a strategical method by incorporating 2D-di in the 3D bulk instead of on the top surface, which effectively confines mobile ions within the grain and suppresses cation phase segregation. This optimization yields stable perovskite solar cells with an extrapolated operational T80 lifetime exceeding 560 hours under harsh conditions (85°C and 2-sun illumination

Revealing Hidden UV Instabilities in Organic Solar Cells by Correlating Device and Material Stability - Classen, Andrej; Heumüller, Thomas; Wabra, Isabell; Gerner, Johannes; He, Yakun; Einsiedler, Lukas; Li, Ning; Matt, Gebhard; Osvet, Andres; Du, Xiaoyan; Hirsch, Andreas; Brabec, Christoph (Advanced Energy Materials, 2019)
With state-of-the-art organic solar cells (OSCs) surpassing 16% efficiency, stability becomes critical for commercialization. In this work, the power of using photoluminescence (PL) measurements on plain films is demonstrated, as well as high-performance liquid chromatography analysis to reveal the origin of UV instabilities in OSCs based on the most commonly used acceptors PC70BM ([6,6]-phenyl-C71-butyric acid methyl ester), ITIC (3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene), and o-IDTBR (indacenodithiophene-based non-fullerene acceptor). The UV dependent stability tests reveal instabilities in solar cells based on PC70BM and ITIC while devices based on o-IDTBR are highly stable even under UV illumination. The analysis of solar cell devices based on charge extraction and sub-bandgap external quantum efficiency only shows the UV-dependent emergence of traps, while PL spectra of plain films on glass allows the disentanglement and identification of individual instabilities in multi-component bulk-heterojunction devices. In particular, the PL analysis demonstrates UV instabilities of PC70BM and ITIC toward the processing additive 1,8 diiodooctane (DIO). The chemical analysis reveals the in-depth mechanism, by providing direct proof of photochemical reactions of PC70BM and ITIC with UV-induced radicals of DIO. Based on this scientific understanding, it is shown how to stabilize PBQ-QF:PC70BM devices.
CRIS-Team Scopus Importer:2019-09-17
Keywords: degradation; diiodooctane; organic solar cells; stability; UV

Revealing Minor Electrical Losses in the Interconnecting Layers of Organic Tandem Solar Cells - Prosa, Mario; Li, Ning; Gasparini, Nicola; Bolognesi, Margherita; Seri, Mirko; Muccini, Michele; Brabec, Christoph (Advanced Materials Interfaces, 2017)
The interconnection layer (ICL) of organic multijunction solar cells represents one of the most delicate parts to ensure an efficient device operation. In view of pushing the efficiencies toward the theoretical limit, the individuation of minor losses affecting the ICL operation is of crucial importance. However, the difficulties arising from its position within the complex device structure typically hamper an accurate and selective investigation of the ICL. Here, a method based on the analysis of the photo-generated current density-voltage (Jph-V) response of solar cells, in the region of bias over the open-circuit voltage, is proved to individuate minor electrical losses within the ICL. Interestingly, the proposed method is demonstrated to effectively operate on tandem substructures, where different ICLs are investigated through the combination of materials having diverse characteristics. Furthermore, the use of a complementary investigation technique based on electroluminescence (EL) analysis allows to distinguish the specific nature of the electrical losses. The combination of Jph-V and EL analyses represents an elegant and advanced approach to shed light on the quality of ICLs in tandem substructures by avoiding the fabrication of the more complex tandem architecture. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: Electrical losses; Electroluminescence; Interconnecting layers; Organic tandem solar cells; Photo-generated current

Revealing Photodegradation Pathways of Organic Solar Cells by Spectrally Resolved Accelerated Lifetime Analysis - Weitz, Paul; Le Corre, Vincent Marc; Du, Xiaoyan; Forberich, Karen; Deibel, Carsten; Brabec, Christoph; Heumüller, Thomas (Advanced Energy Materials, 2022)
A method for organic solar cell (OSC) stability testing is presented that aims to provide more unique insight into the causes of degradation patterns of OSCs. The method involves using monochromatic light at high irradiation doses to accelerate isolated degradation mechanisms while monitoring the device with a series of in-situ steady-state and transient electrical measurements. The experimental results are accompanied by drift-diffusion simulations to localize degradation pathways. PM6:Y6-based OSCs are tested, which are known to show a rather broad range of lifetimes as a function of device architecture, material batches, or degradation conditions. The experiments reveal a degradation mechanism that causes an increased trap-state density inside the PM6:Y6 layer. The transient simulations suggest that these states are formed at or around the interface between the PM6:Y6 and the electron transport layer. Furthermore, the surprisingly dominant impact of the illuminating wavelength on the degradation pattern is evidenced. Lastly, the degradation rate of the devices scales linearly with light intensity, making high intensity and spectrally selective degradation the most promising way to accelerate stability testing for the faster development of stable OSCs.
CRIS-Team Scopus Importer:2022-12-09
Keywords: acceleration; drift-diffusion; organic solar cells; photodegradation; transient; wavelength-dependence

Revealing the Crystallization and Thermal-Induced Phase Evolution in Aromatic-Based Quasi-2D Perovskites Using a Robot-Based Platform - Zhang, Jiyun; Wu, Jianchang; Zhao, Yicheng; Zou, Yuqin; Barabash, Anastasia; Wu, Zhenni; Zhang, Kaicheng; Deng, Can; Elia, Jack; Li, Chaohui; Rocha Ortiz, Juan Sebastian; Liu, Chao; et al. (ACS Energy Letters, 2023)
Introducing large organic cations to form reduced-dimensional (quasi-2D) perovskites has proven to be effective in stabilizing three-dimensional perovskites. In this study, we synthesized 28 Ruddlesden-Popper-type quasi-2D perovskites using four aromatic-based cations (phenylmethylammonium (PMA), phenethylammonium (PEA), phenylpropylammonium (PPA), and phenylbutanammonium (PBA)) and systematically investigated their optoelectronic and structural properties and thermal stability. A counterintuitive finding that longer-chain PPA-based films exhibited relatively poorer stability compared to films with shorter-chain cations has been found. This instability in PPA-based samples is attributed to significant lattice distortion and a mismatched phase between face-sharing trimers, causing intense configurational strain. On the other hand, PBA-containing films maintained robust structural stability due to distinctive crystallization kinetics and a gradual phase-transformation process (from larger-n to lower-n phases) induced by a stronger steric-hindrance effect. Our study sheds light on the complex impact of aromatic-based cations on optoelectronic properties and stability of perovskites, providing guidelines for the rational compositional design engineering of highly stable perovskite material

Revealing the doping density in perovskite solar cells and its impact on device performance - Peña-Camargo, Francisco; Thiesbrummel, Jarla; Hempel, Hannes; Musiienko, Artem; Le Corre, Vincent Marc; Diekmann, Jonas; Warby, Jonathan; Unold, Thomas; Lang, Felix; Neher, Dieter; Stolterfoht, Martin (Applied Physics Reviews, 2022)
Traditional inorganic semiconductors can be electronically doped with high precision. Conversely, there is still conjecture regarding the assessment of the electronic doping density in metal-halide perovskites, not to mention of a control thereof. This paper presents a multifaceted approach to determine the electronic doping density for a range of different lead-halide perovskite systems. Optical and electrical characterization techniques, comprising intensity-dependent and transient photoluminescence, AC Hall effect, transfer-length-methods, and charge extraction measurements were instrumental in quantifying an upper limit for the doping density. The obtained values are subsequently compared to the electrode charge per cell volume under short-circuit conditions (C U bi/e V), which amounts to roughly 1016 cm-3. This figure of merit represents the critical limit below which doping-induced charges do not influence the device performance. The experimental results consistently demonstrate that the doping density is below this critical threshold (∼1012 cm-3, which means â‰ª C U bi/e V) for all common lead-based metal-halide perovskites. Nevertheless, although the density of doping-induced charges is too low to redistribute the built-in voltage in the perovskite active layer, mobile ions are present in sufficient quantities to create space-charge-regions in the active layer, reminiscent of doped pn-junctions. These results are well supported by drift-diffusion simulations, which confirm that the device performance is not affected by such low doping densities.
CRIS-Team Scopus Importer:2022-06-10

Revealing the Morphology of Organic Bulk Heterojunction Solar Cells Using EFTEM and Low‐Energy STEM - Fladischer, Stefanie; Schweizer, Peter; Ameri, Tayebeh; Brabec, Christoph; Spiecker, Erdmann (European Microscopy Congress 2016, 2016)
The morphology of organic bulk heterojunction (BHJ) solar cells decisively influences the device performance and efficiency and therefore is an important factor that needs to be investigated to gain a better understanding and improvement of the devices. Especially the nanoscale morphology of the active layer plays an important role as it determines the charge separation at the interfaces and the percolation pathways to the electrodes. This nanoscale morphology depends not only on the involved materials but also on their molecular weight and their treatment like thermal annealing and solvent vapor annealing.<br
Keywords: organic solar cells; morphology; EFTEM; low-energy STEM

Revealing the strain-associated physical mechanisms impacting the performance and stability of perovskite solar cells - Meng, Wei; Zhang, Kaicheng; Osvet, Andres; Zhang, Jiyun; Gruber, Wolfgang; Forberich, Karen; Meyer, Bernd; Heiß, Wolfgang; Unruh, Tobias; Li, Ning; Brabec, Christoph (Joule, 2022)
Identification and investigation of strain at buried interfaces in halide perovskite photovoltaics are crucial for directing research on the performance and stability of perovskite solar cells. In this work, we find a gradual shift in the band gap of up to 60 meV over a perovskite layer thickness of 300 nm caused by interfacial strain. This graded band gap is desired insofar as it relates to the aspect of device engineering. However, in parallel, the increased defect density causes charge recombination at the buried interface. These two effects compensate for each other, resulting in an overall performance improvement under standard 1 sun illumination. Nevertheless, the disadvantage of enhanced defect density is clearly observed at low-light intensities, where the device performance becomes dominated by charge recombination and ion migration. Moreover, the strained interfaces are proven to induce enhanced defect densities, causing significantly accelerated device degradation under illumination as well as in the dark.
CRIS-Team Scopus Importer:2022-03-18
Keywords: device stability; graded band gap; interface engineering; low-light PV applications; perovskite solar cells; strain engineering

Revealing Trap States in Lead Sulphide Colloidal Quantum Dots by Photoinduced Absorption Spectroscopy - Kahmann, Simon; Sytnyk, Mykhailo; Schrenker, Nadine; Matt, Gebhard; Spiecker, Erdmann; Heiß, Wolfgang; Brabec, Christoph; Loi, Maria A. (Advanced Electronic Materials, 2017)
Due to their large surface to volume ratio, colloidal quantum dots (CQDs) are often considered to exhibit a significant amount of surface defects. Such defects are one possible source for the formation of in-gap states (IGS), which can enhance the recombination of excited carriers, i.e., work as electrical traps. These traps are investigated for lead sulphide CQDs of different size, covered with different ligands using a mid-infrared photoinduced absorption (PIA) technique. The obtained PIA spectra reveal two distinct absorption bands, whose position depends on the particle size, i.e., the electronic confinement in the CQDs. Smaller particles exhibit deeper traps. The chemical nature of the capping ligand does not affect the resulting position other than due to its change in confinement, but better passivating species lead to smaller signals. Furthermore, ligand specific narrow lines observed are superimposed on the broad electronic background of the PIA spectra, which is attributed to Fano resonances caused by the interplay of the narrow molecular vibrations and the continuum of trap states. Mid-infrared photoinduced absorption represents a valuable tool to unravel distributions of IGS in CQDs and allows for an assessment of the quality of ligand exchanged films. These findings have implications for understanding the performances of CQD-based (opto-) electronic devices, such as solar cells, transistors, or quantum dot light emitting diodes, which are limited by frequent carrier trapping events.
Keywords: Colloidal quantum dots; Mid infrared spectroscopy; Molecular vibrations; Pump-probe spectroscopy; Trap states

Reversible Growth of Halide Perovskites via Lead Oxide Hydroxide Nitrates Anchored Zeolitic Imidazolate Frameworks for Information Encryption and Decryption - Zeng, Linxiang; Huang, Xiongjian; Le, Yakun; Zhou, Xinming; Zheng, Wenyan; Brabec, Christoph; Qiao, Xvsheng; Guo, Fei; Fan, Xianping; Dong, Guoping (ACS nano, 2023)
The low formation energies of metal halide perovskites endow them with potential luminescent materials for applications in information encryption and decryption. However, reversible encryption and decryption are greatly hindered by the difficulty in robustly integrating perovskite ingredients into carrier materials. Here, we report an effective strategy to realize information encryption and decryption by reversible synthesis of halide perovskites, on the lead oxide hydroxide nitrates (Pb13O8(OH)6(NO3)4) anchored zeolitic imidazolate framework composites. Benefiting from the superior stability of ZIF-8 in combination with the strong bond between Pb and N evidenced by X-ray absorption spectroscopy and X-ray photoelectron spectroscopy, the as-prepared Pb13O8(OH)6(NO3)4-ZIF-8 nanocomposites (Pb-ZIF-8) can withstand common polar solvent attack. Taking advantage of blade-coating and laser etching, the Pb-ZIF-8 confidential films can be readily encrypted and subsequently decrypted through reaction with halide ammonium salt. Consequently, multiple cycles of encryption and decryption are realized by quenching and recovery of the luminescent MAPbBr3-ZIF-8 films with polar solvents vapor and MABr reaction, respectively. These results provide a viable approach to integrate the state-of-the-art materials perovskites and ZIF for applications in information encryption and decryption films with large scale (up to 6 × 6 cm2), flexibility, and high resolution (approximate 5 μm line width).
CRIS-Team Scopus Importer:2023-03-24
Keywords: blade coating; femtosecond laser etching; lead oxide hydroxide nitrate; perovskite; ZIF-8

Review of SiC crystal growth technology - Wellmann, Peter (Semiconductor Science and Technology, 2018)
have made SiC a unique semiconductor material for power electronic devices. Related to the outstanding physical properties of SiC, the preparation of this material is quite challenging. Processing is carried out at elevated temperatures that require special emphasis on the design of the growth machine and the applied construction materials. Growth inside a closed growth chamber demands the usage of advanced sensors and sophisticated computer simulation of the growth process. The application of advanced 2D and 3D in situ x-ray visualization techniques enables the visualization of the growth process. Reduction of the density of structural defects, a prerequisite for the technical application in power electronic devices, based on fundamental research and understanding of the crystallographic as well as the electronic properties of SiC beyond the knowledge base of standard semiconductor materials.<br
Keywords: crystal growth; technology; silicon carbide

Review of Sublimation Growth of SiC Bulk Crystals - Wellmann, Peter; Arzig, Matthias; Ihle, Jonas; Kollmuß, Manuel; Steiner, Johannes; Mauceri, M.; Crippa, D.; Lavia, F.; Salamon,; Uhlmann, N.; Roder, M.; Danilewsky, A.; et al. (Materials Science Forum, 2022)
The review on bulk growth of SiC includes a basic overview on the widely used physical vapor transport method for processing of 4H-SiC boules as well as the discussion of three current research topics: (a) Sublimation bulk growth of large area, freestanding cubic SiC, (b) in-situ Visualization of the PVT Process using 2D and 3D X-ray based imaging and (c) prediction of dislocation formation and motion in SiC using a continuum model of dislocation dynamics (CDD).
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Keywords: 3C-SiC; 4H-SiC; bulk growth; dislocations; X-ray in-situ visualization

Robot-Based High-Throughput Engineering of Alcoholic Polymer: Fullerene Nanoparticle Inks for an Eco-Friendly Processing of Organic Solar Cells - Xie, Chen; Tang, Xiaofeng; Berlinghof, Marvin; Langner, Stefan; Chen, Shi; Späth, Andreas; Li, Ning; Fink, Rainer; Unruh, Tobias; Brabec, Christoph (ACS Applied Materials and Interfaces, 2018)
Development of high-quality organic nanoparticle inks is a significant scientific challenge for the industrial production of solution processed organic photovoltaics (OPVs) with eco-friendly processing methods. In this work, we demonstrate a novel, robot-based, high throughput procedure performing automatic poly(3-hexylthio-phene-2,5-diyl) and indene-C-60 bisadduct nanoparticle ink synthesis in nontoxic alcohols. A novel methodology to prepare particle dispersions for fully functional OPVs by manipulating the particle size and solvent system was studied in detail. The ethanol dispersion with a particle diameter of around 80-100 nm exhibits reduced degradation, yielding a power conversion efficiency of 4.52%, which is the highest performance reported so far for water/alcohol-processed OPV devices. By successfully deploying the high-throughput robot-based approach for an organic nanoparticle ink preparation, we believe that the findings demonstrated in this work will trigger more research interest and effort on eco-friendly industrial production of OPVs.
Keywords: organic photovoltaics; eco-friendly industrial production; robot-based systems; high-throughput organic nanoparticle synthesis; stable organic nanoparticle inks; organic nanoparticle size control

Robot-Based High-Throughput Screening of Antisolvents for Lead Halide Perovskites - Gu, Ening; Tang, Xiaofeng; Langner, Stefan; Duchstein, Patrick; Zhao, Yicheng; Levchuk, Ievgen; Kalancha, Violetta; Stubhan, Tobias; Hauch, Jens; Egelhaaf, Hans-Joachim; Zahn, Dirk; Osvet, Andres; et al. (Joule, 2020)
Solution-based processing of photovoltaic materials has important advantages, including lower overall costs and easier upscaling of fabrication, where the solvents play an essential role. Antisolvent crystallization technique is often applied to achieve high-quality perovskite materials. However, the basic chemistry of the solvent-antisolvent crystallization is still not well understood. Besides, common antisolvents are toxic, and their number is limited. In this work, a novel robot-based method was used to screen the efficient antisolvents for different solvent-perovskite systems. 336 combinations of perovskite-solvent-antisolvent could be prepared and characterized by the integrated robotic platform in 2 days. In addition, we provided a detailed working mechanism of the solvent-antisolvent crystallization approach. Furthermore, hundreds of potential antisolvents were proposed based on high-throughput screening and simulation. Verification tests match well with theory, and all reported antisolvents used for photovoltaic device optimizations are within our predicted range of the Hansen space, indicating that the predictions are reliable. In terms of solution-processed lead halide perovskite optoelectrical materials, suitable antisolvent is essential for the crystallization and properties of final products. Conventional experiments of antisolvent selections are based on the manual time-consuming trial-error methods, which cannot meet today's increasing demands. In this work, a robot-based method was used to screen the antisolvents for different solvent-perovskite systems in a high-throughput manner to study the influence of interactions among the solvent molecules, cations, metal-halides, and antisolvents, to build an informative database, and to reveal the working mechanism and selection criteria of antisolvents. Besides, simulations based on the screening results provide hundreds of potential antisolvents. Corresponding verification tests evidenced that our predictions are reliable and vital for designing future efficient mixed solvent systems for the fabrication of perovskite optoelectrical materials. A robotic platform is adopted to conduct a comprehensive solvent engineering for making lead halide perovskites in a high-throughput manner. Deeper insights into the working mechanisms and selection criteria of antisolvents are investigated and summarized. In addition, a reliable antisolvent database is established, and verification tests match well with the theory. Furthermore, our work provides significant guidance for designing functional and environment-friendly mixed solvent systems to fabricate high-quality perovskite materials or devices.
CRIS-Team Scopus Importer:2020-08-21
Keywords: antisolvents; automated research; high-throughput method; lead halide complexes; lead halide perovskite; solvent engineering

Robust nonfullerene solar cells approaching unity external quantum efficiency enabled by suppression of geminate recombination - Baran, Derya; Gasparini, Nicola; Wadsworth, Andrew; Tan, Ching Hong; Wehbe, Nimer; Song, Xin; Hamid, Zeinab; Zhang, Weimin; Neophytou, Marios; Kirchartz, Thomas; Brabec, Christoph; Durrant, James R.; et al. (Nature Communications, 2018)
Nonfullerene solar cells have increased their efficiencies up to 13%, yet quantum efficiencies are still limited to 80%. Here we report efficient nonfullerene solar cells with quantum efficiencies approaching unity. This is achieved with overlapping absorption bands of donor and acceptor that increases the photon absorption strength in the range from about 570 to 700 nm, thus, almost all incident photons are absorbed in the active layer. The charges generated are found to dissociate with negligible geminate recombination losses resulting in a short-circuit current density of 20 mA cm(-2) along with open-circuit voltages >1 V, which is remarkable for a 1.6 eV bandgap system. Most importantly, the unique nano-morphology of the donor:acceptor blend results in a substantially improved stability under illumination. Understanding the efficient charge separation in nonfullerene acceptors can pave the way to robust and recombination-free organic solar cells.

Role of Polymer Fractionation in Energetic Losses and Charge Carrier Lifetimes of Polymer: Fullerene Solar Cells - Baran, Derya; Vezie, Michelle S.; Gasparini, Nicola; Deledalle, Florent; Yao, Jizhong; Schroeder, Bob C.; Bronstein, Hugo; Ameri, Tayebeh; Kirchartz, Thomas; Mcculloch, Iain; Nelson, Jenny; Brabec, Christoph (Journal of Physical Chemistry C, 2015)
Nonradiative recombination reduces the open-circuit voltage relative to its theoretical limit and leads to reduced luminescence emission at a given excitation. Therefore, it is possible to correlate changes in luminescence emission with changes in open-circuit voltage and in the charge carrier lifetime. Here we use luminescence studies combined with transient photovoltage and differential charging analyses to study the effect of polymer fractionation in indacenoedithiophene-co-benzothiadiazole (IDTBT):fullerene solar cells. In this system, polymer fractionation increases electroluminescence emission at the same injection current and reduces nonradiative recombination. High-molecular-weight and fractionated IDTBT polymers exhibit higher carrier lifetime-mobility product compared to that of their nonfractionated analogues, resulting in improved solar cell performance. (Graph Presented).
Keywords: Engineering controlled terms: Carrier lifetime; Charge carriers; Fullerenes; Light; Luminescence; Open circuit voltage; Polymers Differential charging; Electroluminescence emission; High molecular weight; Luminescence emission; Non-radiative recombinations; Polymer fractionation; Solar cell performance; Transient photovoltage Engineering main heading: Solar cells

Roll to roll compatible fabrication of inverted organic solar cells with a self-organized charge selective cathode interfacial layer - Zhang, Hong; Tan, Wan-Yi; Fladischer, Stefanie; Ke, Lili; Ameri, Tayebeh; Li, Ning; Turbiez, Mathieu; Spiecker, Erdmann; Zhu, Xu-Hui; Cao, Yong; Brabec, Christoph (Journal of Materials Chemistry A, 2016)
We successfully demonstrate a simple approach to printing efficient, inverted organic solar cells (OSCs) with a self-organized charge selective cathode interface layer based on the small-molecule Phen-NaDPO. Different from previous studies, Phen-NaDPO molecules were blended into a polymer/fullerene blend, comprising a low bandgap diketopyrrolopyrrole-quinquethiophene alternating copolymer pDPP5T-2 and phenyl-C-butyric acid methyl ester (PCBM), and processed by doctor blading in air. We observed a spontaneous, surface energy driven migration of Phen-NaDPO towards the ZnO interface and a subsequent formation of electron selective and barrier free extraction contacts. In the presence of 0.5 wt% Phen-NaDPO, a PCE of 5.4% was achieved for the inverted device based on an ITO/ZnO cathode. Notably, the photovoltaic performances remained at the same level with increasing the Phen-NaDPO concentration in the active layer from 0.25 to 1 wt%. Furthermore, this approach could be proven to effectively work with other cathodes such as bare ITO and ITO/AZO. The self-organization of Phen-NaDPO through spontaneous vertical phase separation is mainly attributed to its high surface energy and strong interaction with the cathode material. The present results highlight that a self-organized cathode interfacial material processed from a "ternary" active layer is fully compatible with the requirements for roll-to-roll fabrication of inverted organic solar cells.
Keywords: Engineering controlled terms: Butyric acid; Cathodes; Electrodes; Interfacial energy; Molecules; Organic solar cells; Phase separation Alternating copolymer; Cathode interfacial layers; Diketopyrrolopyrroles; High surface energy; Inverted organic solar cells; Photovoltaic performance; Roll-to-roll fabrication; Vertical phase separations Engineering main heading: Solar cells

Roll-to-Roll Deposition of Wide-Bandgap CsFAPbBr3 Perovskite Solar Cells in Ambient Air with Optimized Ink Formulation - Jafarzadeh, Farshad; Dong, Lirong; Jang, Dongju; Wagner, Michael; Koch, Giulio; Qiu, Shudi; Feroze, Sarmad; García Cerrillo, José; Brabec, Christoph; Di Carlo, Aldo; Brunetti, Francesca; Egelhaaf, Hans-Joachim; et al. (Solar RRL, 2024)
The growing demand for sustainable energy solutions has made the development of scalable, efficient, and cost-effective perovskite solar cells (PSCs) increasingly important. Wide-bandgap perovskites (WB-PSCs) stand out due to their efficiency in low-light conditions and their use in tandem solar cells. WB-PSCs are currently behind conventional PSCs in upscaling, with limited success in printing wide bandgap PSCs. Developing upscaling methods is essential to fully realize their potential in the renewable energy sector. This research addresses the development of roll-to-roll (R2R) slot-die coating of Cs0.05FA0.95PbBr3-based WB-PSCs by focusing on improving the film formation process and ink formulation. By adding optimal concentration of CsBr and performing in situ characterization, we obtained Cs0.05FA0.95PbBr3 films with enhanced morphology and crystallinity in ambient conditions (50% RH), without inducing secondary phase formation. In addition, slot-die coating defects are eliminated through introducing DMSO: Butanol (9:1) solvent system. The R2R coated wide-bandgap PSCs reaches a power conversion efficiency (PCE) of up to 8.97% under 1-sun conditions and 18.3% PCE under indoor conditions. The corresponding R2R coated modules with a 5 × 5 cm2 active area achieve a PCE of 5.8%, representing a crucial step towards the high-throughput, cost-effective production of perovskite solar modules.
CRIS-Team Scopus Importer:2024-10-11
Keywords: ambient deposition; ink formulation; roll-to-roll; slot-die coating; wide-bandgap perovskite solar cells

Rough Electrode Creates Excess Capacitance in Thin-Film Capacitors - Torabi, Solmaz; Cherry, Megan; Duijnstee, Elisabeth A; Le Corre, Vincent Marc; Qiu, Li; Hummelen, Jan C; Palasantzas, George; Koster, L Jan Anton (ACS Applied Materials and Interfaces, 2017)
The parallel-plate capacitor equation is widely used in contemporary material research for nanoscale applications and nanoelectronics. To apply this equation, flat and smooth electrodes are assumed for a capacitor. This essential assumption is often violated for thin-film capacitors because the formation of nanoscale roughness at the electrode interface is very probable for thin films grown via common deposition methods. In this work, we experimentally and theoretically show that the electrical capacitance of thin-film capacitors with realistic interface roughness is significantly larger than the value predicted by the parallel-plate capacitor equation. The degree of the deviation depends on the strength of the roughness, which is described by three roughness parameters for a self-affine fractal surface. By applying an extended parallel plate capacitor equation that includes the roughness parameters of the electrode, we are able to calculate the excess capacitance of the electrode with weak roughness. Moreover, we introduce the roughness parameter limits for which the simple parallel-plate capacitor equation is sufficiently accurate for capacitors with one rough electrode. Our results imply that the interface roughness beyond the proposed limits cannot be dismissed unless the independence of the capacitance from the interface roughness is experimentally demonstrated. The practical protocols suggested in our work for the reliable use of the parallel-plate capacitor equation can be applied as general guidelines in various fields of interest.
Keywords: parallel-plate capacitor equation; interface roughness; dielectric constant; capacitance; thin-film capacitors

Round-Robin studies as a method for testing and validating high-effi ciency ito-free polymer solar cells based on roll-to-roll-coated highly conductive and transparent flexible substrates - Larsen-Olsen, Thue T.; Machui, Florian; Lechene, Balthazar; Berny, Stephane; Angmo, Dechan; Sondergaard, Roar; Blouin, Nicolas; Mitchell, William; Tierney, Steven; Cull, Tobias; Tiwana, Priti; Meyer, Frank; et al. (Advanced Energy Materials, 2012)
Photovoltaic cells based on organic and polymer materials (OPVs) are celebrated as being a possible solution to the energy needs of the future, [ 1b ] and, with record effi ciencies having breached the 10% milestone accompanied by emerging involvement from the materials industry, expectations are rapidly approaching reality. [ 1c ] However, in order to move OPVs beyond the individual laboratory and into a generally applied setting, scientists need to limit the gap between carefully prepared hero devices and the large-scale manufacture of thousands of devices. We propose that this is done by urgently attending to the challenges of scalability and reproducibility. In this communication, we demonstrate an approach using round-robin testing as a method to validate effi ciency measurements of OPVs based on semitransparent electrodes on fl exible substrates, with and without indium tin oxide (ITO). ITO-free substrates were rollto- roll coated under ambient conditions and were truly scalable. Our results demonstrate inherent uncertainties in the device-effi ciency data, with variations in the carefully measured effi ciency data for the same device between highly qualifi ed laboratories as high as 25%, depending on the substrate and its active area. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Round-Robin Studies on Roll-Processed ITO-free Organic Tandem Solar Cells Combined with Inter-Laboratory Stability Studies - Livi, Francesco; Sondergaard, Roar R.; Andersen, Thomas R.; Roth, Berenger; Gevorgyan, Suren; Dam, Henrik F.; Carle, Jon E.; Helgesen, Martin; Spyropoulos, Georgios; Adams, Jens; Ameri, Tayebeh; Brabec, Christoph; et al. (Energy Technology, 2015)
Roll-processed, indium tin oxide (ITO)-free, flexible, organic tandem solar cells and modules have been realized and used in round-robin studies as well as in parallel inter-laboratory stability studies. The tandem cells/modules show no significant difference in comparison to their single-junction counterparts and the use of round-robin studies as a consensus tool for evaluation of organic solar cell parameters is judged just as viable for the tandem solar cells as for single-junction devices. The inter-laboratory stability studies were conducted according to testing protocols ISOS-D-2, ISOS-D-3, and ISOS-L-2, and in spite of a much more complicated architecture the organic tandem solar cells show no significant difference in stability in comparison to their single-junction counterparts. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: ITO-free; Photovoltaics; Roll processing; Stability; Tandem solar cells

Sb2Se3Thin-Film Growth by Solution Atomic Layer Deposition - Koch, Vanessa; Charvot, Jaroslav; Cao, Yuanyuan; Hartmann, Claudia; Wilks, Regan G.; Kundrata, Ivan; Minguez Bacho, Ignacio; Gheshlaghi, Negar; Hoga, Felix; Stubhan, Tobias; Alex, Wiebke; Pokorný, Daniel; et al. (Chemistry of Materials, 2022)
We establish solution atomic layer deposition (sALD) for the controlled growth of pure Sb2Se3 thin films under mild conditions, namely, room temperature and atmospheric pressure. Upscaling this process yields Sb2Se3 thin films with high homogeneity over large-area (4″) substrates. Annealing of the initially amorphous material leads to highly crystalline and smooth Sb2Se3 thin films. Removing the constraints of thermal stability and sufficient volatility in sALD compared to traditional gas-phase ALD opens up a broad choice of precursors and allows us to examine a wide range of Se2- precursors, of which some exhibit facile synthetic routes and allow us to tune their reactivity for optimal experimental ease of use. Moreover, we demonstrate that the solvent used in sALD represents an additional, attractive tool to influence and tailor the reactivity at the liquid-solid interface between the precursors and the surface.
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Scalable, ambient atmosphere roll-to-roll manufacture of encapsulated large area, flexible organic tandem solar cell modules - Andersen, Thomas R.; Dam, Henrik F.; Hosel, Markus; Helgesen, Martin; Carle, Jon E.; Larsen-Olsen, Thue T.; Gevorgyan, Suren A.; Andreasen, Jens W.; Adams, Jens; Li, Ning; Machui, Florian; Spyropoulos, Georgios; et al. (Energy and Environmental Science, 2014)
Inline printing and coating methods have been demonstrated to enable a high technical yield of fully roll-to-roll processed polymer tandem solar cell modules. We demonstrate generality by employing different material sets and also describe how the ink systems must be carefully co-developed in order to reach the ambitious objective of a fully printed and coated 14-layer flexible tandem solar cell stack. The roll-to-roll methodologies involved are flexographic printing, rotary screen printing, slot-die coating, X-ray scattering, electrical testing and UV-lamination. Their combination enables the manufacture of completely functional devices in exceptionally high yields. Critical to the ink and process development is a carefully chosen technology transfer to industry method where first a roll coater is employed enabling contactless stack build up, followed by a small roll-to-roll coater fitted to an X-ray machine enabling in situ studies of wet ink deposition and drying mechanisms, ultimately elucidating how a robust inline processed recombination layer is key to a high technical yield. Finally, the transfer to full roll-to-roll processing is demonstrated. This journal is © the Partner Organisations 2014.
Keywords: Engineering controlled terms: Coatings; Manufacture; Technology transfer; Testing Ambient atmosphere; Flexographic printing; Functional devices; Polymer tandem solar cells; Process development; Recombination layers; Roll-to-roll processing; Rotary screen printing Engineering main heading: Solar cells GEOBASE Subject Index: coating; photovoltaic system; polymer; solar power; technological development

Scanning electron microscopical examination of the impact of laser patterning on microscopic inhomogeneities of Cu(In,Ga)(Se,S)2 absorbers produced by rapid thermal processing - Künecke, Ulrike; Hölzing, Astrid; Jost, Stefan; Lechner, Robert; Vogt, Helmut; Heiss, Andreas; Palm, Jörg; Hock, Rainer; Wellmann, Peter (Thin Solid Films, 2013)
Laser scribing of the Mo back electrode is commonly applied to define the cell structure of Cu(In,Ga)(Se,S) (CIGSSe) thin film solar cells. The patterning process was performed on laboratory samples using ns and ps pulse length laser processes. After structuring, CIGSSe absorbers were processed by rapid thermal processing (RTP) of stacked elemental layer precursors. Microscopic inhomogeneities were investigated on different sample positions. For samples structured with ns pulse, the absorber morphology in the laser line vicinity is different as compared to the morphology in the unstructured cell area. Scanning electron microscopy and energy-dispersive X-ray spectroscopy show significant changes in the absorber grain size and chemical composition. Close to the laser line, the typically observed Ga accumulation on the back contact is less pronounced and more Ga is incorporated closer to the surface leading to a smaller grain size. The observed changes are attributed to partial damaging of a diffusion barrier between glass and Mo induced by the ns laser process, which allows diffusion of sodium from the glass substrate into the absorber during RTP. The enhanced Ga incorporation closer to the surface is an indication for the influence of sodium on the local phase development during RTP. The damages of the diffusion barrier can be effectively prevented by the application of a ps laser scribing process. CIGSSe absorbers processed on samples structured with ps pulse length do not show the described microscopic inhomogeneities around the laser line. © 2013 Elsevier B.V.
Keywords: Cu(In; Ga)(Se; S)2; Chalcopyrite; Solar cells; Laser patterning; Sodium; SEM; Mo back contact; SEL-RTP

Scintillators based on CdWO 4 and CdWO 4: Bi single crystalline films - Zorenko, Yuriy; Gorbenko, Vitaliy; Voznyak, Taras; Konstankevych, Ivan; Savchyn, Volodymyr; Batentschuk, Miroslaw; Winnacker, Albrecht; Brabec, Christoph (IEEE Transactions on Nuclear Science, 2012)
This research is directed on creating by liquid phase epitaxy the single crystalline film scintillators based on undoped and Bi doped CdWO compounds as well as the phoswich detector based on CdWO : Bi or CdWO films CdWO or CdWO : Bi crystals epitaxial structures. The luminescent and scintillation properties of the undoped and Bi doped (in a concentration range of 0.04-0.25 at. %) CdWO films, grown by LPE method from Na WO flux, were compared with the properties of CdWO bulk crystal analogs, grown from melts by the Czochralski method. Using the traditional luminescence spectroscopy and the luminescence spectroscopy under excitation by pulsed synchrotron radiation with energy in the fundamental absorption range of CdWO host, we have also examined the nature of different emission centers and studied energy transfer processes from tungstate hosts to Bi ions and defect centers in CdWO and CdWO : Bi films and their crystal analogs. © 2012 IEEE.
Keywords: Bi dopant; liquid phase epitaxy; luminescence; scintillators; single crystals and single crystalline films

Selective Growth of Layered Perovskites for Stable and Efficient Photovoltaics - Cho, Kyung Taek; Grancini, Giulia; Lee, Yonghui; Oveisi, Emad; Ryu, Jaehoon; Almora Rodriguez, Osbel; Tschumi, Manuel; Schouwink, Pascal Alexander; Seo, Gabseok; Heo, Sung; Park, Jucheol; Jang, Jyongsik; et al. (Energy and Environmental Science, 2018)
Perovskite solar cells (PSCs) are promising alternative to clean energy because of their high-power conversion efficiency (PCE) and low materials and processing cost. However, their poor stability and operation still limits their practical applications. Here we design an innovative approach to control the surface growth of a low-dimensional perovskite layer on top of a bulk three-dimensional (3D) perovskite film. This results in a structured perovskite interface where a distinct layered low dimensional perovskite is engineered on top of the 3D film. Structural and optical properties of the cells are realized. When embodying the low dimensional perovskite layer, the photovoltaic cells exhibit an enhanced PCE of 20.1% on average, when compared to pristine 3D perovskite. In addition,<br

Self-assembled microstructured polymeric and ceramic surfaces - Woiton, Michael; Heyder, Madeleine; Laskowsky, Alexandra; Stern, Edda; Scheffler, Michael; Brabec, Christoph (Journal of the European Ceramic Society, 2011)
Self-assembled microstructures were manufactured by dip coating of substrates with unfilled and filler-loaded preceramic polymer mixtures in the presence of a solvent and a non-solvent. The nature of the polymers was characterized by their solubility parameters. Variation of the polymer/polymer ratio and the volume fraction of the solvent and/or non-solvent led to different surface structures. Studies of the structure formation mechanism indicate that demixing processes of the polymers are responsible for self-assembly in filler-free mixtures. In filler-loaded mixtures the structure formation process, however, is more complex. The micro-structured polymeric coatings obtained from filler loaded systems were converted into polymer derived ceramic coatings under shape retention. High specific surface areas were measured after thermal conversion. © 2011 Elsevier Ltd.
Keywords: Films; Porosity; Precursors-organic; Self-assembly; SiC; Surfaces

Self-assembly construction of a homojunction of Sn-Pb perovskite using an antioxidant for all-perovskite tandem solar cells with improved efficiency and stability - Lin, Zhuojia; Chen, Jianwei; Duan, Chenghao; Fan, Kezhou; Li, Jiong; Zou, Shibing; Zou, Feilin; Yuan, Ligang; Zhang, Zheng; Zhang, Kaicheng; Lam, Man Yu; Aleksandr, Sergeev A.; et al. (Energy and Environmental Science, 2024)
All-perovskite tandem solar cells (PTSCs) demonstrate higher power conversion efficiency (PCE) and lower levelized cost of electricity than single-junction perovskite solar cells (PSCs). However, narrow bandgap (NBG) sub-cells with a Sn-Pb alloy cause severe p-type self-doping by surface oxidized Sn4+ to generate substantial energy loss and device degradation. Here, we developed a one-step self-assembly strategy to construct a p/p− homojunction of Sn-Pb perovskite using the antioxidant 4-trifluoromethylphenylhydrazine hydrochloride (TFPHCl) and prepared highly efficient and stable NBG PSCs. Self-floating TFPH cations allowed effective defect passivation and inhibition of Sn2+-Sn4+ oxidation, leading to a weak p-type surface (p−). Hence, the as-formed p/p− homojunction in turn accelerated the charge separation and reduced the non-radiative recombination. TFPHCl-modified NBG PSCs reached a stabilized PCE of 23.09% with an open-circuit voltage (Voc) of 0.88 V and excellent operational stability over 780 hours. Coupled with wide bandgap (WBG) subcells, TFPHCl-modified PTSCs ultimately attained an optimal PCE of 27.42% with long-term operational stability over 450 hours.
CRIS-Team Scopus Importer:2024-09-06

Self-assembly of colloidal single-layer carbon nitride - Stroyuk, Oleksandr; Raievska, Oleksandra; Brabec, Christoph; Dzhagan, Volodymyr; Havryliuk, Yevhenii; Zahn, Dietrich R. T. (Nanoscale, 2022)
We introduce a new concept of a "bottom-to-top" design of intercalate carbon nitride compounds based on the effects of self-assembly of colloidal single-layer carbon nitride (SLCN) sheets stabilized by tetraethylammonium hydroxide NEt4OH upon ambient drying of the water solvent. These effects include (i) formation of stage-1 intercalates of NEt4OH during the ambient drying of SLCN colloids on glass substrates and (ii) the spontaneous formation of layered hexagonally-shaped networks of SLCN sheets on freshly-cleaved mica surfaces. The dynamics of the intercalate formation was followed by in situ X-ray diffraction allowing different stages to be identified, including the deposition of a primary "wet" intercalate of hydrated NEt4OH and the gradual elimination of excessive water during its ambient drying. The intercalated NEt4+ cations show a specific "flattened" conformation allowing the dynamics of formation and structure of the intercalate to be probed by vibrational spectroscopies. The two-dimensional self-assembly on mica is assumed to be driven both by the internal hexagonal symmetry of heptazine units and by a templating effect of the mica surface.
CRIS-Team WoS Importer:2022-08-26

Self-driving AMADAP laboratory: Accelerating the discovery and optimization of emerging perovskite photovoltaics - Zhang, Jiyun; Wu, Jianchang; Stroyuk, Oleksandr; Raievska, Oleksandra; Lüer, Larry; Hauch, Jens; Brabec, Christoph (Mrs Bulletin, 2024)
The development of new solar materials for emerging perovskite photovoltaics poses intricate multi-objective optimization challenges in a large high-dimensional composition and parameter space, with in some cases, millions of potential candidates to be explored. Solving it necessitates reproducible, user-independent laboratory work and intelligent preselection of innovative experimental methods. Materials Acceleration Platforms (MAPs) seamlessly combine robotic materials synthesis, characterization, and AI-driven data analysis, enabling the exploration of new materials. They revolutionize material development by replacing trial-and-error methods with precise, rapid experimentation and generating high-quality data for training machine learning (ML) algorithms. Device Acceleration Platforms (DAPs) focus on optimizing functional energy films and multilayer stacks. Unlike MAPs, DAPs concentrate on refining processing conditions for predetermined materials, crucial for disordered semiconductors. By fine-tuning processing parameters, DAPs significantly advance disordered semiconductor devices such as emerging photovoltaics. This article examines recent advancements in automated laboratories for perovskite material discovery and photovoltaics device optimization, showcasing in-house-developed MAPs and a DAP. These platforms cover the entire value chain, from materials to devices, addressing optimization challenges through robot-based high-throughput experimentation (HTE). Ultimately, a self-driven Autonomous Material and Device Acceleration Platforms (AMADAP) laboratory concept is proposed for autonomous functional solar material discovery using AI-guided combinational approaches.
CRIS-Team Scopus Importer:2025-02-04
Keywords: Autonomous research; Chemical synthesis; Machine learning; Perovskites; Photovoltaic; Semiconducting

Self-Healing Cs3Bi2Br3I6 Perovskite Wafers for X-Ray Detection - Daum, Manuel; Deumel, Sarah; Sytnyk, Mykhailo; Afify, Hany A.; Hock, Rainer; Eigen, Andreas; Zhao, Baolin; Halik, Marcus; These, Albert; Matt, Gebhard; Brabec, Christoph; Tedde, Sandro F.; et al. (Advanced Functional Materials, 2021)
Self-healing of defects imposed by external stimuli such as high energy radiation is a possibility to sustain the operational lifetime of electronic devices such as radiation detectors. Cs3Bi2Br3I6 polycrystalline wafers are introduced here as novel X-ray detector material, which not only guarantees a high X-ray stopping power due to its composition with elements with high atomic numbers, but also outperforms other Bi-based semiconductors in respect to detector parameters such as detection limit, transient behavior, or dark current. The polycrystalline wafers represent a size scalable technology suitable for future integration in imager devices for medical applications. Most astonishingly, aging of these wafer-based devices results in an overall improvement of the detector performance—dark currents are reduced, photocurrents are increased, and one of the most problematic properties of X-ray detectors, the base line drift is reduced by orders of magnitude. These aging induced improvements indicate self-healing effects which are shown to result from recrystallization. Optimized synthetic conditions also improve the as prepared X-ray detectors; however, the aged device outperforms all others. Thus, self-healing acts in Cs3Bi2Br3I6 as an optimization tool, which is certainly not restricted to this single compound, it is expected to be beneficial also for many further polycrystalline ionic semiconductors.
CRIS-Team Scopus Importer:2021-08-27
Keywords: bismuth halides; lead-free perovskites; photoconductors; self-healing; X-ray detection

Semitransparent Organic Light Emitting Diodes with Bidirectionally Controlled Emission - Bronnbauer, Carina; Osvet, Andres; Brabec, Christoph; Forberich, Karen (ACS Photonics, 2016)
Semitransparent OLEDs are a candidate for large-area eco-friendly light sources that can be integrated into building facades, suggesting colorful windows that become luminescent if the OLED is switched on. However, since the light is emitted in two directions, smart light engineering has to be implemented to direct the light into a preferred direction and to prevent for instance huge energetic losses to the outside of a building. We introduce an unprecedented device architecture, composed of a dielectric mirror attached to a semitransparent OLED. Such a system features a dual functionality that depends on the viewing direction: changing the color perception and/or enhancing the light directionality while still preserving a high overall device transparency. First, we motivate the potential of this concept with a theoretical study, showing that broad modifications in the color range can be realized via device optimization and that the maximum possible emission enhancement of the OLED is limited only by the transparency of the interfacial layers and the electrodes. Then, experimental investigations with a semitransparent yellow OLED (transparency = 58.2%) in combination with six different dielectric mirrors validate the theoretical results. Retaining the same color perception, up to 80% of the total emitted light can be directed toward one side while the color is modified at the other side of the device stack. Here, modifications from yellow to purple to dark or light blue can be realized.
Keywords: color modification; dielectric mirror; fully printed; light management; OLED; semitransparent

Semitransparent Organic Photovoltaic Devices: Interface/Bulk Properties and Stability Issues - Paci, Barbara; Righi Riva, Flavia; Generosi, Amanda; Guaragno, Marco; Mangiacapre, Emanuela; Brutti, Sergio; Wagner, Michael; Distler, Andreas; Egelhaaf, Hans Joachim (Nanomaterials, 2024)
In the present work, an insight on the morpho/structural properties of semitransparent organic devices for buildings’ integrated photovoltaics is presented, and issues related to interface and bulk stability are addressed. The organic photovoltaic (OPV) cells under investigation are characterized by a blend of PM6:Y6 as a photo-active layer, a ZnO ETL (electron transporting layer), a HTL (hole transporting layer) of HTL-X and a transparent electrode composed by Ag nanowires (AgNWs). The devices’ active nanomaterials, processed as thin films, and their mutual nanoscale interfaces are investigated by a combination of in situ Energy Dispersive X-ray Reflectometry (EDXR) and ex situ Atomic Force Microscopy (AFM), X-ray Diffraction (XRD) and micro-Raman spectroscopy. In order to discriminate among diverse concomitant aging pathways potentially occurring upon working conditions, the effects of different stress factors were investigated: light and temperature. Evidence is gained of an essential structural stability, although an increased roughness at the ZnO/PM6:Y6 interface is deduced by EDXR measurements. On the contrary, an overall stability of the system subjected to thermal stress in the dark was observed, which is a clear indication of the photo-induced origin of the observed degradation phenomenon. Micro-Raman spectroscopy brings light on the origin of such effect, evidencing a photo-oxidation process of the active material in the device, using hygroscopic organic HTL, during continuous illumination in ambient moisture conditions. The process may be also triggered by a photocatalytic role of the ZnO layer. Therefore, an alternative configuration is proposed, where the hygroscopic HTL-X is replaced by the inorganic compound MoOx. The results show that such alternative configuration is stable under light stress (solar simulator), suggesting that the use of Molybdenum Oxide, limiting the photo-oxidation of the bulk PM6:Y6 active material, can prevent the cell from degradation.
CRIS-Team Scopus Importer:2024-02-16
Keywords: Ag nanowires; in-situ characterization; interfaces; morphology; OPVs; structural properties

Semitransparent organic photovoltaic modules with Ag nanowire top electrodes - Guo, Fei; Kubis, Peter; Przybilla, Thomas; Spiecker, Erdmann; Forberich, Karen; Brabec, Christoph (International Society for Optical Engineering; 1999, 2014)
Semitransparent organic photovoltaic (OPV) cells are promising for applications in transparent architectures where their opaque counterparts are not suitable. Manufacturing of large-area modules without performance losses compared to their lab-scale devices is a key step towards practical applications of this PV technology. In this paper, we report the use of solution-processed silver nanowires as top electrodes and fabricate semitransparent OPV modules based on ultra-fast laser scribing. Through a rational choice of device architecture in combination with high-precision laser patterning, we demonstrate efficient semitransparent modules with comparable performance as compared to the reference devices.
Keywords: semitransparent organic solar cells; organic photovoltaic modules; silver nanowires; laser patterning

Semitransparent polymer solar cells - Guo, Fei; Ameri, Tayebeh; Forberich, Karen; Brabec, Christoph (Polymer International, 2013)
This perspective discusses the choice of semiconducting photoactive polymers toward high efficiencies of semitransparent polymer solar cells and stresses several promising alternative transparent electrodes to ITO and their processing methods. Bulk heterojunction based polymer:fullerene solar cells have attracted intensive research interest both in academic and industrial communities in the last two decades, mainly related to their potential low-cost production process. A power conversion efficiency of over 10% has been reported recently, making the commercialization of this clean and cheap solar energy convertor a realistic prospect for the near future. The intrinsic features of semitransparency and color tunability of the thin polymeric photoactive films are the greatest asset for polymer solar cells. Recently, aesthetic semitransparent polymer solar cells (ST-PSCs) that can be integrated into transparent windows, roofs, glass and other semitransparent architectural elements have received much attention. In this perspective paper, we present the progress in achieving high performance ST-PSCs, discuss the requirements for transparent electrodes, focusing on alternatives to tin-doped indium oxide, and address the challenges ahead to make ST-PSC viable for real applications. © 2013 Society of Chemical Industry.
Keywords: Bulk heterojunction; OPV; Polymer solar cells; Semitransparent; Silver nanowire

Sensitive Direct Converting X-Ray Detectors Utilizing Crystalline CsPbBr3 Perovskite Films Fabricated via Scalable Melt Processing - Matt, Gebhard; Levchuk, Ievgen; Knüttel, Judith; Dallmann, Johannes; Osvet, Andres; Sytnyk, Mykhailo; Tang, Xiaofeng; Elia, Jack; Hock, Rainer; Heiß, Wolfgang; Brabec, Christoph (Advanced Materials Interfaces, 2020)
Here the fabrication of an inorganic metal-halide perovskite CsPbBr3 based X-ray detector is reported utilizing a simple, scalable, and cost-sensitive melt processing directly on substrate of any size. X-ray diffraction analysis on the several 100 mm thick melt processed films confirms crystalline domains in the cm(2) range. The CsPbBr3 film features a resistance of 8.5 G omega cm and a hole mobility of 18 cm(2) V-1 s(-1). An X-ray to current conversion rate of 1450 mC Gy(air)(-1) cm(-2) at an electric field of 1.2 x 10(4) V cm(-1) and a detection limit in the sub mu Gy(air) s(-1) regime is demonstrated. The high crystallinity and chemical purity of the melt processed CsPbBr3 films are suggested to be responsible for a performance which is on par to current state-of-the-art Cd(Zn)Te based X-ray detector technology.
Keywords: X-ray detection; metal-halide perovskites; photophysics

Separating the Influence of Material Composition and Local Defects on the Voc of CIGS Solar Modules - Hepp, Johannes; Vetter, Andreas; Hofbeck, Bernhard; Camus, Christian; Hauch, Jens; Brabec, Christoph (33rd European Photovoltaic Solar Energy Conference and Exhibition, 2017)
In spite of the steadily improved quality of co-evaporated Cu(In,Ga)Se2 absorber layers, the existence of local defects affecting the module performance in large area production can still be an issue. Generally, both, lateral composition gradients and point defects can be found in those layers. We show the necessity to separate these two influences and propose two measurement techniques in order to asses the effect of the material and the defects individually. In oder to quantify the theoretical defect-free open circuit voltage (Voc), given by the material composition, we used luminescence spectroscopy. The additional effect on the Voc originating from local defects was determined using dark lock-in thermography. The combination of both these methods enables a local prediction of a module’s Voc. In the following, we conduct an indepth analysis of the determination of the material composition and its impact on the resulting Voc.
Keywords: Defects; Monitoring; Spectroscopy; Electroluminescence; CIGS

Sequential Deposition of High-Quality Photovoltaic Perovskite Layers via Scalable Printing Methods - Guo, Fei; He, Wenxin; Qiu, Shudi; Wang, Chuan; Liu, Xianhu; Forberich, Karen; Brabec, Christoph; Mai, Yaohua (Advanced Functional Materials, 2019)
Sequential deposition is demonstrated as an effective technology for preparation of high-performance perovskite solar cells based on lab-scale spin coating. However, devices fabricated by scalable methods are lagging far behind their state-of-the-art spin-coated counterparts, largely due to the difficulty in obtaining high-quality thin films of perovskites crystallized from printed precursors. Here, a generic strategy that allows sequential deposition of dense and uniform perovskite films via two-step blade coating is reported. The rational selection of solvent combined with a mild vacuum extraction process enables us to produce uniform lead iodide (PbI2) films over large areas. Significantly, the resulting PbI2 films possess a mesoporous structure that is highly beneficial for the insertion reaction with methylammonium iodide (MAI). It is further identified that the deposition temperature of MAI plays an important role in determining the morphology and crystallinity of the perovskite films. Solar cells using these sequentially bladed perovskite layers yield efficiencies over 16% with high fill factors up to 78%. These results represent important progress toward the largescale deposition of perovskite thin films for practical applications<br
Keywords: perovskite; scalable printing; sequential deposition; solar cells

Series vs parallel connected organic tandem solar cells: Cell performance and impact on the design and operation of functional modules - Etxebarria, Ikerne; Furlan, Alice; Ajuria, Jon; Fecher, Frank W.; Voigt, Monika; Brabec, Christoph; Wienk, Martijn M.; Slooff, Lenneke; Veenstra, Sjoerd; Gilot, Jan; Pacios, Roberto (Solar Energy Materials and Solar Cells, 2014)
Tandem solar cells are the best approach to maximize the light harvesting and adjust the overall absorption of the cell to the solar irradiance spectrum. Usually, the front and back subcells are connected in series in two-terminal device (2T) designs which require a current matching between both subcells in order to avoid potential losses. Alternatively, they can also be connected in parallel giving rise to a three terminal connection (3T). In principle, both designs have their assets and drawbacks in terms of device performance, design and materials' characterization. In this letter, we theoretically and experimentally confront both designs with each other (2T and 3T). Theoretical estimations show a maximum PCE of 15% for 2T and about 13% for 3T structures with ideal bandgaps for the front and back cell. However, 3T tandem devices can yield higher efficiencies than 2T for some specific material combinations whose theoretical values are between 10% and 12%. Therefore, other aspects related to the fabrication feasibility are studied in order to analyze the most convenient approach for module development. The need of a conducting interlayer restricts the width of the cell and causes a 3% reduction in the geometrical fill factor of the module in comparison to the 2T approach. The R2R processing of modules with 3T cells would also require an additional laser step. Finally, a couple of existing material combinations have been experimentally implemented into 2T and 3T tandem devices. The limitation imposed by their specific and non-ideal bandgaps restricts the efficiency to around 7%, considerably below the ideal case. © 2014 Elsevier B.V.
Keywords: R2R module processing; Tandem organic solar cells; Three-terminal parallel connection; Two-terminal series connection

Shape-Controlled Solution-Epitaxial Perovskite Micro-Crystal Lasers Rivaling Vapor Deposited Ones - Afify, Hany A.; Rehm, Viktor; Barabash, Anastasia; These, Albert; Zhang, Jiyun; Osvet, Andres; Schüßlbauer, Christoph; Thiel, Dominik; Ullrich, Tobias; Dierner, Martin; Przybilla, Thomas; Will, Johannes; et al. (Advanced Functional Materials, 2022)
Epitaxial growth methods usually need dedicated equipment, high energy consumption to maintain pure vacuum conditions and evaporation of source materials, and elevated substrate temperatures. Solution epitaxial growth requires nothing of that but is rarely used because the achieved microstructures are of low quality, not homogeneous, and finally exhibit worse performances in devices. Here, an antisolvent-vapor-assisted-crystallization of metal-halide-perovskites as a method overcoming these disadvantages is demonstrated. The methylammonium lead tribromide exhibits van-der-Waals type of epitaxial growth on mica substrates, resulting in micro-crystallites whose shape can be controlled to be either triangular micro-prism or micro-cuboid. These micro-crystallites act as optical resonators supporting various optical modes and lasing is achieved under optical excitation with low thresholds and record high environmental stability. Selecting suitable resonators from a large variety of sizes allows control of mode spacing and finally mono-mode operation, considered to be an important feature of semiconductor laser devices. The achieved results are essentially competitive to those obtained by vapor phase epitaxial microstructures, highlighting that epitaxy of high-quality optoelectronic device structures is feasible by minimum technological efforts and energy consumption, which are of increasing importance considering issues such as global warming and the current energy crisis.
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Short-wave infrared colloidal quantum dot photodetectors on silicon - Hu, Chen; Gassenq, Alban; Justo, Yolanda; Yakunin, Sergii; Heiß, Wolfgang; Hens, Zeger; Roelkens, Gunther (8631, 2013)
In this paper, two kinds of colloidal quantum dots, PbS and HgTe, are explored for SWIR photodetectors application. The colloidal dots are prepared by hot injection chemical synthesis, with organic ligands around the dots keeping them stable in solution. For the purpose of achieving efficient carrier transport between the dots in a film, these long organic ligands are replaced by shorter, inorganic ligands. We report uniform, ultra-smooth colloidal QD films without cracks realized by dip-coating and corresponding ligand exchange on a silicon substrate. Metal-free inorganic ligands, such as OH - and S 2-, are investigated to facilitate the charge carrier transport in the film. Both PbS and HgTe-based quantum dot photoconductors were fabricated on interdigitated gold electrodes. For PbS-based detectors a responsivity of 200A/W is measured at 1.5μm, due to the large internal photoconductive gain. A 2.2μm cut-off wavelength for PbS photodetectors and 2.8μm for HgTe quantum dot photodetectors are obtained. © 2013 SPIE.
Keywords: colloidal quantum dots; photoconductor; solid-state ligand exchange

Shy Organic Photovoltaics: Digitally Printed Organic Solar Modules With Hidden Interconnects - Maisch, Philipp; Tam, Kai Cheong; Schilinsky, Pavel; Egelhaaf, Hans-Joachim; Brabec, Christoph (Solar RRL, 2018)
One of the biggest attractions of the organic photovoltaics (OPV) technology is the easiness with which it can be integrated. However, despite its semitransparency and wide variety of colors, a major unresolved challenge is to fabricate optically inconspicuous organic photovoltaic modules (OPV-M) that can be integrated into visually demanding products. This is dominantly due to the visual obstruction from Z-interconnection lines inherent to module processing with classical patterning methods. We now present for the first time a solution to this problem, which utilizes a visually seamless interconnection method to elegantly minimize the conspicuity of the interconnection regime. We realize such invisible interconnects by inkjet printing highly conductive silver lines, which penetrate the solar cell stack and form an electrical connection between adjacent cells. A combined characterization approach utilizing in-depth electrical characterization and finite element (FEM) simulation rationalizes the excellent electrical cell-to-cell contact established with this interconnection technology. We combine this technology with a variable-geometry module design into an innovative digital inkjet printing platform for the production of state-of-the art but visually attractive solar modules. The full potential of this concept is demonstrated by a fully inkjet printed arbitrarily shaped OPV-M portrait<br
Keywords: inkjet printing; organic photovoltaics; printed electronics; shy photovoltaics; upscaling

SiC crystal growth from the vapor and liquid phase - Hofmann, Heinz-Dieter; Bickermann, Matthias; Ebling, Dirk; Epelbaum, Boris; Kadinski, Lev; Selder, Markus; Straubinger, Thomas; Weingärtner, Roland; Wellmann, Peter; Winnacker, Albrecht (Materials Research Society Symposium - Proceedings, 2001)
The status of SiC vapor growth technique (PVT) is reviewed and related innovative aspects are introduced. Problems of the preparation of SiC crystals with uniform electronic properties are addressed, especially the growth of semiinsulating SiC. An overview about the performance of numerical modeling is given as tool for the optimization of the PVT process. Development activities in the field of liquid phase processing for the preparation of SiC bulk crystals and micropipe healing are presented. Finally recent results on the present understanding of filamentary void formation/elimination (micropipes, macrodefects) are summarize

SiC epitaxial structure growth: evaluation and modeling - Nishizawa, Shin-Ichi; Wellmann, Peter; Pons, Michel (Wide Band Gap Materials and New Developments, 2006)

SiC single crystal growth by a modified physical vapor transport technique - Wellmann, Peter; Desperrier, Patrick; Müller, Ralf; Straubinger, Thomas; Winnacker, Albrecht; Baillet, F.; Blanquet, E.; Dedulle, J.M.; Pons, Michel (Journal of Crystal Growth, 2005)
We have developed a modified physical vapor transport (M-PVT) growth technique for the preparation of SiC single crystals which makes use of an additional gas pipe in order to control the gas phase composition of the conventional physical vapor transport (PVT) configuration. We discuss the experimental implementation of the extra gas pipe by comparing crystal growth runs under various gas flow conditions with numerical simulations. The potential of the M-PVT growth method will be demonstrated by showing the improved doping characteristics when performing nitrogen, phosphorus and aluminum doping of SiC using the additional gas pipe for dopant supply. (C) 2004 Elsevier B.V. All rights reserved.
Keywords: Doping; Computer simulation; Growth from vapor; Semiconducting silicon compounds

Side-Chain Engineering for Enhancing the Properties of Small Molecule Solar Cells: A Trade-off Beyond Efficiency - Min, Jie; Cui, Chaohua; Heumüller, Thomas; Fladischer, Stefanie; Cheng, Xiao; Spiecker, Erdmann; Li, Yongfang; Brabec, Christoph (Advanced Energy Materials, 2016)
Three small molecules with different substituents on bithienyl-benzo[1,2-b:4,5-b′]dithiophene (BDTT) units, BDTT-TR (meta-alkyl side chain), BDTT-O-TR (meta-alkoxy), and BDTT-S-TR (meta-alkylthio), are designed and synthesized for systematically elucidating their structure–property relationship in solution-processed bulk heterojunction organic solar cells. Although all three molecules show similar molecular structures, thermal properties and optical band gaps, the introduction of meta-alkylthio-BDTT as the central unit in the molecular backbone substantially results in a higher absorption coefficient, slightly lower highest occupied molecular orbital level and significantly more efficient and balanced charge transport property. The bridging atom in the meta-position to the side chain is found to impact the microstructure formation which is a subtle but decisive way: carrier recombination is suppressed due to a more balanced carrier mobility and BDTT based devices with the meta-alkylthio side chain (BDTT-S-TR) show a higher power conversion efficiency (PCE of 9.20%) as compared to the meta-alkoxy (PCE of 7.44% for BDTT-TR) and meta-alkyl spacer (PCE of 6.50% for BDTT-O-TR). Density functional density calculations suggest only small variations in the torsion angle of the side chains, but the nature of the side chain linkage is further found to impact the thermal as well as the photostability of corresponding devices. The aim is to provide comprehensive insight into fine-tuning the structure–property interrelationship of the BDTT material class as a function of side chain engineering.
Keywords: absorption coefficient; microstructure formation; photostability; side chain engineering; structure-property relationships

Silicon Carbide and Related Materials for Energy Saving Applications—Select Papers from E-MRS 2019—Symposium “Silicon Carbide and Related Materials for Energy Saving Applications" - Wellmann, Peter; La Via, F.; Jennings, Mike (2019)
SYMPOSIUM X on Silicon Carbide & Related Materials focuses electronic materials for energy saving that are of particular interest to meet the accelerating demand of the global energy consumption. Engineering of the wide band-gap semiconductor silicon carbide plays a key role because it provides excellent physical properties that go beyond the semiconductor silico
Keywords: silicon carbide; wide bandgap semiconductors; energy saving

Silicon carbide as a semiconductor material for high temperature, high power and optoelectronics - Winnacker, Albrecht; Hofmann, Heinz-Dieter; Wellmann, Peter (Proceedings of the third Vietnam-German Workshop on Physics and Engineering, 2000)

Silicon carbide CVD for electronic device applications - Wellmann, Peter; Pons, Michel (Chemical Vapor Deposition, 2006)
Keywords: Silicon carbide; CVD; Electronic device application

Silicon carbide growth: C/Si ratio evaluation and modeling - Pons, Michel; Nishizawa, Shin-Ichi; Wellmann, Peter; Blanquet, E.; Chaussende, D.; Dedulle, J.M.; Madar, R. (Materials Science Forum, 2009)
Modeling and simulation of the SiC growth processes, Physical Vapor Transport (PVT), Chemical Vapor Deposition (CVD) and hybrid techniques, are sufficiently mature to be used as a training tool for engineers as well as a growth machine design tool, e.g. when building new process equipment or up-scaling old ones. It is possible (i) to simulate accurately temperature and deposition distributions, as well as doping (ii) to quantify the limiting phenomena, (iii) to understand the important role of different precursors in CVD and hydrogen additions in PVT. The first conclusion of this paper is the importance of the "effective" C/Si ratio during CVD epitaxy in hot-wall reactors and its capability to explain the doping concentrations. The second conclusion is the influence of the C/Si ratio in alternative bulk growth technique involving gas additions. Preliminary results show that fine tuning of H2 or precursor additions allow a better control of concentrations of residual and intentional dopin
Keywords: Modeling; Simulation; Growth; Mass transport; C/Si ratio

Silicon Carbide Growth: C/Si Ratio Evaluation and Modeling - Pons, Michel; Wellmann, Peter; Nishizawa, Shin-Ichi; Blanquet, E.; Dedulle, J.M.; Chaussende, D. (Materials Research Society Symposium - Proceedings, 2006)
Modeling and simulation of the SiC growth processes, Physical Vapor Transport (PVT), Chemical Vapor Deposition (CVD) and hybrid techniques, are sufficiently mature to be used as a training tool for engineers as well as a growth machine design tool, e.g. when building new process equipment or up-scaling old ones. It is possible (i) to simulate accurately temperature and deposition distributions, as well as doping (ii) to quantify the limiting phenomena, (iii) to understand the important role of different precursors in CVD and hydrogen additions in PVT. The first conclusion of this paper is the importance of the "effective" C/Si ratio during CVD epitaxy in hot-wall reactors and its capability to explain the doping concentrations. The second conclusion is the influence of the C/Si ratio in alternative bulk growth technique involving gas additions. Preliminary results show that fine tuning of H2 or precursor additions allow a better control of concentrations of residual and intentional dopin
Keywords: chemical vapor deposition; CVD; crystal growth; simulation

Silicon nitride and intrinsic amorphous silicon double antireflection coatings for thin-film solar cells on foreign substrates - Li, Da; Kunz, Thomas; Wolf, Nadine; Liebig, Jan Philipp; Wittmann, Stephan; Ahmad, Taimoor; Hessmann, Maik T.; Auer, Richard; Göken, Mathias; Brabec, Christoph (Thin Solid Films, 2015)
Hydrogenated intrinsic amorphous silicon (a-Si:H) was investigated as a surface passivationmethod for crystalline silicon thin film solar cells on graphite substrates. The results of the experiments, including quantumefficiency and current density-voltage measurements, show improvements in cell performance. This improvement is due to surface passivation by an a-Si:H(i) layer, which increases the open circuit voltage and the fill factor. In comparison with our previous work, we have achieved an increase of 0.6% absolute cell efficiency for a 40 μm thick 4 cm2 aperture area on the graphite substrate. The optical properties of the SiNx/a-Si:H(i) stack were studied using spectroscopic ellipsometer techniques. Scanning transmission electron microscopy inside a scanning electron microscope was applied to characterize the cross section of the SiNx/a-Si:H(i) stack using focus ion beam preparatio
Keywords: Amorphous silicon; Crystalline silicon thin film; Double layer antireflection coating; Focus ion beam; Graphite substrate; Scanning transmission electron microscopy; Surface passivation

Silicon/organic hybrid heterojunction infrared photodetector operating in the telecom regime - Bednorz, Mateusz; Matt, Gebhard; Glowacki, Eric D.; Fromherz, Thomas; Brabec, Christoph; Scharber, Markus C.; Sitter, Helmut; Sariciftci, N. Serdar (Organic Electronics, 2013)
The authors report on the fabrication of a silicon/organic heterojunction based IR photodetector. It is demonstrated that an Al/p-Si/perylene-derivative/ Al heterostructure exhibits a photovoltaic effect up to 2.7 μm (0.46 eV), a value significantly lower than the bandgap of either material. Although the devices are not optimized, at room temperature a rise time of 300 ns, a responsivity of ≈0.2 mA/W with a specific detectivity of D ≈ 7 × 10 Jones at 1.55 μm is found. The achieved responsivity is two orders of magnitude higher compared to our previous efforts [1,2]. It will be outlined that the photocurrent originates from an absorption mechanism involving excitation of an electron from the Si valence band into the extended LUMO state in the perylene-derivative, with possible participation of intermediate localized surface state in the organic material. The non-invasive deposition of the organic interlayer onto the Si results in compatibility with the CMOS process, making the presented approach a potential alternative to all inorganic device concepts.© 2013 Elsevier B.V. All rights reserved.
Keywords: Hybrid system; Infrared spectroscopy; Organic electronics; Photo-detector

Silver Electrodes for Organic Solar Cells Printed via Laser-Induced Forward Transfer - Bibrack, Max; Distler, Andreas; Wagner, Michael; Forberich, Karen; Brabec, Christoph; Egelhaaf, Hans-Joachim (Energy Technology, 2025)
Laser-induced forward transfer (LIFT) is presented as a new, contactless, and roll-to-roll compatible method for the deposition of silver top electrodes for organic solar cells (OSCs). Employing a nanosecond laser, highly reflective silver electrodes are printed by LIFT onto OSCs with P3HT:o-IDTBR bulk heterojunction layers. Upon optimization of ink composition, source film thickness, and laser parameters, the resulting organic solar cells reach efficiencies of more than 5%, which are similar to those of reference devices with vapor-deposited silver electrodes.
CRIS-Team Scopus Importer:2025-02-04
Keywords: laser-induced forward transfer process; nanosecond laser; organic photovoltaics; printable electrodes; silver nanoparticles

Simplifying contact-layer design for high-throughput printing of flexible perovskite photovoltaics - Dong, Lirong; Qiu, Shudi; Feroze, Sarmad; Wagner, Michael; Kasian, Olga; Peisert, Heiko; Kosasih, Felix U.; Ducati, Caterina; García Cerrillo, José; Tian, Jingjing; Li, Chaohui; Jang, Dongju; et al. (Energy and Environmental Science, 2024)
The realization of scalable roll-to-roll production processes for metal-halide perovskite modules is a necessary development for transferring developments and technologies from the lab to the fab. Before that, it is imperative to close the efficiency gap not only between the devices fabricated on rigid substrates versus flexible substrates, but also between solar cells to solar modules. In this regard, a critical assessment of device architectures that are more compatible to scalable fabrication is needed. Obviously, the adaption to mass manufacturing must not negatively impact device performance and operational stability. Here, by investigating the properties of printed fullerene-based phosphonic acid dipole interface layers, we establish simplified self-assembled monolayer (SAM) based n-i-p architectures without any charge extraction layers other than SAMs, which are easily processed and are thus ideally suited for mass production. We show that a contact-layer design with a printed fullerene-based SAM that has phosphonic acid is sufficient to provide good charge selectivity and to minimize interface recombination at the bottom electrode. We further show that the same SAM molecule can be used as a p-type interface material on top of the perovskite. This simplified contact-layer design, which is based on one material for both hole and electron work-function adaption is successfully integrated into our fully printed module process comprising the deposition of a carbon top electrode. The achieved open-circuit voltage exceeds 1.1 V, and the fill factor surpasses 70%, highlighting the potential of this novel interface design concept for both rigid and flexible substrates.
CRIS-Team Scopus Importer:2024-09-06

SIMsalabim: An open-source drift-diffusion simulator for semiconductor devices - Koopmans, Marten; Le Corre, Vincent Marc; Koster, L Jan Anton (Journal of Open Source Software, 2022)

Simulation of optical Properties of percolation type electrode for thin film solar cells with silver nanowires - Yan, Shuai; Krantz, Johannes; Pflaum, Christoph; Brabec, Christoph (Photonics for Solar Energy Systems IV, 2012)
Silver nanowire films are a newly introduced choice for transparent electrodes in thin film solar cells. Simulation is an adequate and economic method to analyse and predict the optical properties of these films. We simulate the optical behavior of such films by solving Maxwell equations. The simulation technique is a finite integration technique (FIT) combined with a time harmonic inverse iteration method (THIIM) to handle the negative permittivity of silver. Parallel computation on high performance computers(HPC) is used to meet the large computational requirement of the problem. In agreement to preliminary experimental results, the simulation results show that transmission of light is larger than expected by a simple ray-tracing model. © 2012 SPIE.
UnivIS-Import:2015-04-16:Pub.2012.tech.IMMD.lsinfs.simula_8
Keywords: Ag NW films; Maxwell equations; Optical simulation; Parallel computation; Transparent electrodes

Simulation of perovskite thin layer crystallization with varying evaporation rates - Majewski, M.; Qiu, Shudi; Ronsin, O.; Lüer, Larry; Le Corre, Vincent Marc; Du, Tian; Brabec, Christoph; Egelhaaf, Hans-Joachim; Harting, J. (Materials Horizons, 2024)
Perovskite solar cells (PSC) are promising potential competitors to established photovoltaic technologies due to their superior efficiency and low-cost solution processability. However, the limited understanding of the crystallization behaviour hinders the technological transition from lab-scale cells to modules. In this work, advanced phase field (PF) simulations of solution-based film formation are used for the first time to obtain mechanistic and morphological information that is experimentally challenging to access. The well-known transition from a film with many pinholes, for a low evaporation rate, to a smooth film, for high evaporation rates, is recovered in simulation and experiment. The simulation results provide us with an unprecedented understanding of the crystallization process. They show that supersaturation and crystallization confinement effects determine the final morphology. The ratio of evaporation to crystallization rates turns out to be the key parameter driving the final morphology. Increasing this ratio is a robust design rule for obtaining high-quality films, which we expect to be valid independently of the material type.
CRIS-Team Scopus Importer:2024-11-22

Single-Component Organic Solar Cells with Competitive Performance - He, Yakun; Li, Ning; Brabec, Christoph (Organic Materials, 2021)
Organic semiconductors with chemically linked donor and acceptor units can realize charge carrier generation, dissociation and transport within one molecular architecture. These covalently bonded chemical structures enable single-component organic solar cells (SCOSCs) most recently to start showing specific advantages over binary or multi-component bulk heterojunction concepts due to simplified device fabrication and a dramatically improved microstructure stability. The organic semiconductors used in SCOSCs can be divided into polymeric materials, that is, double-cable polymers, di-block copolymers as well as donor–acceptor small molecules. The nature of donor and acceptor segments, the length and flexibility of the connecting linker and the resultant nanophase separation morphology are the levers which allow optimizing the photovoltaic performance of SCOSCs. While remaining at 1–2% for over a decade, efficiencies of SCOSCs have recently witnessed significant improvement to over 6% for several materials systems and to a record efficiency of 8.4%. In this mini-review, we summarize the recent progress in developing SCOSCs towards high efficiency and stability, and analyze the potential directions for pushing SCOSCs to the next efficiency milestone.
Keywords: double-cable polymers; di-block copolymers; donor–acceptor small molecules; single-component organic solar cells; photovoltaic performance; device stability

Single Crystalline Films of Ce3+-Doped Y3MgxSiyAl5−x−yO12 Garnets: Crystallization, Optical, and Photocurrent Properties - Gorbenko, Vitaliy; Zorenko, Tetiana; Shakhno, Anna; Popielarski, Pawel; Osvet, Andres; Batentschuk, Miroslaw; Fedorov, Alexander; Mahlik, Sebastian; Lesniewski, Tadeusz; Majewska, Natalia; Zorenko, Yuriy (Materials, 2023)
This research focuses on LPE growth, and the examination of the optical and photovoltaic properties of single crystalline film (SCF) phosphors based on Ce3+-doped Y3MgxSiyAl5−x−yO12 garnets with Mg and Si contents in x = 0–0.345 and y = 0–0.31 ranges. The absorbance, luminescence, scintillation, and photocurrent properties of Y3MgxSiyAl5−x−yO12:Ce SCFs were examined in comparison with Y3Al5O12:Ce (YAG:Ce) counterpart. Especially prepared YAG:Ce SCFs with a low (x, y < 0.1) concentration of Mg2+ and Mg2+–Si4+ codopants also showed a photocurrent that increased with rising Mg2+ and Si4+ concentrations. Mg2+ excess was systematically present in as-grown Y3MgxSiyAl5−x−yO12:Ce SCFs. The as-grown SCFs of these garnets under the excitation of α–particles had a low light yield (LY) and a fast scintillation response with a decay time in the ns range due to producing the Ce4+ ions as compensators for the Mg2+ excess. The Ce4+ dopant recharged to the Ce3+ state after SCF annealing at T > 1000 °C in a reducing atmosphere (95%N2 + 5%H2). Annealed SCF samples exhibited an LY of around 42% and similar scintillation decay kinetics to those of the YAG:Ce SCF counterpart. The photoluminescence studies of Y3MgxSiyAl5−x−yO12:Ce SCFs provide evidence for Ce3+ multicenter formation and the presence of an energy transfer between various Ce3+ multicenters. The Ce3+ multicenters possessed variable crystal field strengths in the nonequivalent dodecahedral sites of the garnet host due to the substitution of the octahedral positions by Mg2+ and the tetrahedral positions by Si4+. In comparison with YAG:Ce SCF, the Ce3+ luminescence spectra of Y3MgxSiyAl5−x−yO12:Ce SCFs greatly expanded in the red region. Using these beneficial trends of changes in the optical and photocurrent properties of Y3MgxSiyAl5−x−yO12:Ce garnets as a result of Mg2+ and Si4+ alloying, a new generation of SCF converters for white LEDs, photovoltaics, and scintillators could be developed.
CRIS-Team Scopus Importer:2023-03-24
Keywords: Ce; liquid-phase epitaxy; luminescence; Mg; phosphor converters; photocurrent; scintillators; single crystalline films

Single Domain 3C-SiC Growth on Off-Oriented 4H-SiC Substrates - Jokubavicius, Valdas; Yazdi, Gholam R.; Liljedahl, Rickard; Ivanov, Ivan G.; Sun, Jianwu; Liu, Xinyu; Schuh, Philipp; Wilhelm, Martin; Wellmann, Peter; Yakimova, Rositsa; Syväjärvi, Mikael (Crystal Growth & Design, 2015)
We investigated the formation of structural defects in thick (similar to 1 mm) cubic silicon carbide (3C-SiC) layers grown on off-oriented 4H-SiC substrates via a lateral enlargement mechanism using different growth conditions. A two-step growth process based on this technique was developed, which provides a trade-off between the growth rate and the number of defects in the 3C-SiC layers. Moreover, we demonstrated that the two-step growth process combined with a geometrically controlled lateral enlargement mechanism allows the formation of a single 3C-SiC domain which enlarges and completely covers the substrate surface. High crystalline quality of the grown 3C-SiC layers is confirmed using high resolution X-ray diffraction and low temperature photoluminescence measurements.
Keywords: 3C-SiC; lateral enlargement; sublimation epitaxy; geometrical control

Single-Layer Carbon Nitride as an Efficient Metal-Free Organic Electron-Transport Material with a Tunable Work Function - Saboor, Abdus; Stroyuk, Oleksandr; Raievska, Oleksandra; Liu, Chao; Hauch, Jens; Brabec, Christoph (Advanced Functional Materials, 2024)
Single-layer carbon nitride (SLCN) is introduced as a metal-free organic electron transport material (ETL) for organic solar cells, delivering a performance comparable to that of the benchmark nanocrystalline ZnO. SLCN is produced in the form of stable aqueous inks and can serve as an efficient electron transport layer for three different types of active layers, showing high stability to photodegradation. A lower conductivity of SLCN films as compared to ZnO is counter-balanced by their higher transparency and lower light scattering losses. The SLCN ETL provides a unique opportunity to tune the work function from ca. −4.1 to −4.6 eV by varying the annealing temperature due to partial thermal oxidation of the SLCN film. The PL band position follows the oxidation-induced changes of the work function allowing PL properties of SLCN to be used to predict the PV efficiency. The 2D structure of SLCN coupled with unique structural and compositional variability, and tunability of the work function show a high promise for emerging organic PV devices.
CRIS-Team Scopus Importer:2024-03-15
Keywords: 2D materials; charge transport materials; organic solar cells; polyheptazine

Single molecular precursor ink for AgBiS2 thin films: synthesis and characterization - Gu, Ening; Lin, Xianzhong; Tang, Xiaofeng; Matt, Gebhard; Osvet, Andres; Hou, Yi; Jäger, Sebastian; Xie, Chen; Karl, André; Hock, Rainer; Brabec, Christoph (Journal of Materials Chemistry C, 2018)
Recently, AgBiS2 has been demonstrated to be a promising non-toxic, earth-abundant absorber material for solar energy application. In this work, a novel route to deposit AgBiS2 thin films from single molecular precursor ink is presented. It is found that the amount of thiourea has a crucial impact on the formulation of a stable molecular ink. Understanding the coordination chemistry of the molecular precursor ink is important for getting better control over the thin film processing. With the assistance of Raman spectroscopy, possible complexation mechanisms and general coordination states within the molecular ink are studied. In addition, the influence of ink composition as well as the annealing temperature on the structure and morphology of resulting AgBiS2 films is systematically investigated. It is found that the crystallinity and particle size increase with higher annealing temperature. The obtained AgBiS2 thin films show a cubic structure with a preferred orientation in [111] direction. Optical and electrical measurements demonstrate that the obtained AgBiS2 is an indirect band gap material, which features two transition mechanisms with an indirect band gap of around 0.87 eV and a direct one of around 1.21 eV. The high absorption coefficient, low Urbach energy and fast transient photoconductivity confirm its potential as an absorber for photovoltaic applications.

Single-Walled Carbon Nanotubes as an Additive in Organic Photovoltaics: Effects on Carrier Generation and Recombination Dynamics - Abudulimu, Abasi; Eckstein, Klaus; El Gemayel, Mirella; Namal, Imge; Phillips, Adam B.; Ellingson, Randy J.; Heben, Michael J.; Hertel, Tobias; Meier, Sebastian B.; Lüer, Larry (Solar RRL, 2022)
Employing single-walled carbon nanotubes (SWNTs) as an additive in the active layer of organic photovoltaics (OPV) to improve charge extraction is gaining weight in the research community. While SWNTs can transport charge carriers orders of magnitudes faster than conventional polymers, they also quench excitons and trap-free charges, reducing device performance. Such influences of SWNTs on OPV device performance remain inadequately explored and incompletely understood. Herein, the impact of SWNTs, enriched in (6,5) chirality, on the charge generation and extraction properties of two different OPV devices is studied by femtosecond-microsecond transient absorption spectroscopy and transient photovoltage/photocurrent techniques. It is shown that depending on the donor material properties (e.g., energetics), SWNTs can reduce carrier generation by quenching the excitons and increase carrier recombination through trapping processes. Then, by performing an analytical calculation of the currentvoltage characteristics of the devices using the parameters determined via the transient measurements, it is shown that the increased recombination also relates to morphological changes induced by the SWNTs. These results shed light on the performance limiting factors of the SWNTs when incorporated into the active layer of the solar cells. This work thus can accelerate the blend optimization process for high-performance organic solar cells.
CRIS-Team WoS Importer:2022-02-11

Site-specific assessment of mechanical loads on photovoltaic modules from meteorological reanalysis data - Camus, Christian; Offermann, Pascal; Weissmann, Martin; Buerhop, Claudia; Hauch, Jens; Brabec, Christoph (Solar Energy, 2019)
This work demonstrates the capability of meteorological reanalysis data for estimating mechanical stresses due to wind gusts on photovoltaic modules. Besides the immediate power loss caused by the inactive solar cell areas within the module, the influence of cracks induced by such mechanical loads on the ageing and degradation behavior of PV modules is in the focus of current PV reliability research. To choose and/or design the optimum module for a given deployment site at the most economical cost, the mechanical loads the module will be exposed to during its service life need to be estimated. Hence, this paper introduces a new methodology for assessing and deducing site-specific mechanical load scenarios which are expected to be imposed on photovoltaic modules by wind gusts for a given location. The approach presented here is based on the linear calibration of meteorological reanalysis data with publicly available and standardized high-quality surface weather station data of local weather services. In this fashion, site-specific mechanical load scenarios can be deduced for virtually any site covered by the respective reanalysis data set. These scenarios can be used for developing site-specific module qualification tests, thereby providing a methodology enabling climate-specific module designs or specifications. This methodology can also be transferred to virtually any location and other climate and weather parameters such as snow loads, UV dose, etc. Hence a complete assessment of all weather-related degradation scenarios could be deduced eventually.
CRIS-Team Scopus Importer:2019-07-16
Keywords: Degradation; Forecast; Mechanical load; Photovoltaics; Reanalysis; Wind gusts

Six metal cations in one double perovskite: exploring complexity of chloride elpasolites by high-throughput experimentation - Stroyuk, Oleksandr; Raievska, Oleksandra; Daum, Manuel; Hauch, Jens; Brabec, Christoph (Journal of Materials Chemistry C, 2024)
A high-throughput screening of lead-free double chloride perovskites Cs2MIMIIICl6 is performed combining combinatorial robot-assisted synthesis with accelerated structural and spectral characterizations. The screening encompasses about 350 elpasolite compounds with broad variations of the MIII site, including combinations of two (Bi + In, Bi + Sb, and In + Sb) and three cations (In + Bi + Sb and Fe + Bi + In). The robot-assisted open-environment synthesis protocol allows the double perovskites with these MIII combinations and Ag+/Na+-occupied MI site to be produced using a general routine in the form of single-phase microcrystalline solid solutions with reliably controlled composition. The high-throughput screening revealed a series of non-additive effects arising from the combination of multiple cations on the MIII site, including a “volcano”-shaped dependence of the photoluminescence quantum yield of Cs2(Ag,Na)(Bi,In)Cl6 elpasolites on Ag/Na and Bi/In ratio and band-bowing effects in the compositional dependences of the bandgaps of perovskites with Bi + Sb, In + Bi + Sb, and Fe + Bi + In combinations. In the latter case, the accelerated screening resulted in the double chloride perovskites with an unusually low indirect bandgap of 1.64 eV.
CRIS-Team Scopus Importer:2024-06-14

Size-Dependent Charge Transfer in Blends of PbS Quantum Dots with a Low-Gap Silicon-Bridged Copolymer - Itskos, Grigorios; Papagiorgis, Paris; Tsokkou, Demetra; Othonos, Andreas; Hermerschmidt, Felix; Economopoulos, Solon P.; Yarema, Maksym; Heiß, Wolfgang; Choulis, Stelios (Advanced Energy Materials, 2013)
The photophysics of bulk heterojunctions of a high-performance, low-gap silicon-bridged dithiophene polymer with oleic acid capped PbS quantum dots (QDs) are studied to assess the material potential for light harvesting in the visible-and IR-light ranges. By employing a wide range of nanocrystal sizes, systematic dependences of electron and hole transfer on quantum-dot size are established for the first time on a low-gap polymer-dot system. The studied system exhibits type II band offsets for dot sizes up to ca. 4 nm, whch allow fast hole transfer from the quantum dots to the polymer that competes favorably with the intrinsic QD recombination. Electron transfer from the polymer is also observed although it is less competitive with the fast polymer exciton recombination for most QD sizes studied. The incorporation of a fullerene derivative provides efficient electron-quenching sites that improve interfacial polymer-exciton dissociation in ternary polymer-fullerene-QD blends. The study indicates that programmable band offsets that allow both electron and hole extraction can be produced for efficient light harvesting based on this low-gap polymer-PbS QD composite.
Keywords: organic semiconductors; photodetectors; photophysics; quantum dots; solar cells

SnO2-in-Polymer Matrix for High-Efficiency Perovskite Solar Cells with Improved Reproducibility and Stability - Wei, Jing; Guo, Fengwan; Wang, Xi; Xu, Kun; Lei, Ming; Liang, Yongqi; Zhao, Yicheng; Xu, Dongsheng (Advanced Materials, 2018)
Understanding interfacial loss and the ways to improving interfacial property is critical to fabricate highly efficient and reproducible perovskite solar cells (PSCs). In SnO2-based PSCs, nonradiative recombination sites at the SnO2-perovskite interface lead to a large potential loss and performance variation in the resulting photovoltaic devices. Here, a novel SnO2-in-polymer matrix (i.e., polyethylene glycol) is devised as the electron transporting layer to improve the film quality of the SnO2 electron transporting layer. The SnO2-in-polymer matrix is fabricated through spin-coating a polymer-incorporated SnO2 colloidal ink. The polymer is uniformly dispersed in SnO2 colloidal ink and promotes the nanoparticle disaggregation in the ink. Owing to polymer incorporation, the compactness and wetting property of SnO2 layer is significantly ameliorated. Finally, photovoltaic devices based on Cs(0.05)FA(0.81)MA(0.14)PbI(2.55)Br(0.45) perovskite sandwiched between SnO2 and Spiro-OMeTAD layer are fabricated. Compared with the averaging power conversion efficiency of 16.2% with 1.2% deviation for control devices, the optimized devices exhibit an improved averaging efficiency of 19.5% with 0.25% deviation. The conception of polymer incorporation in the electron transporting layer paves a way to further increase the performance of planar perovskite solar cells.
Keywords: perovskite solar cells; reproducibility; SnO2-in-polymer matrix; stability

Solar cell fabricated on welded thin flexible silicon - Hessmann, Maik Thomas; Kunz, Thomas; Ahmad, Taimoor; Li, Da; Wittmann, Stephan; Riecke, Arne; Ebser, Jan; Terheiden, Barbara; Cvecek, Kristian; Schmidt, Michael; Auer, Richard; Brabec, Christoph (EPJ Photovoltaics, 2015)
We present a thin-film crystalline silicon solar cell with an AM1.5 efficiency of 11.5% fabricated on welded 50 μm thin silicon foils. The aperture area of the cell is 1.00 cm 2 . The cell has an open-circuit voltage of 570 mV, a short-circuit current density of 29.9 mA cm − 2 and a fill factor of 67.6%. These are the first results ever presented for solar cells on welded silicon foils. The foils were welded together in order to create the first thin flexible monocrystalline band substrate. A flexible band substrate offers the possibility to overcome the area restriction of ingot-based monocrystalline silicon wafers and the feasibility of a roll-to-roll manufacturing. In combination with an epitaxial and layer transfer process a decrease in production costs can be achieved.
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Solar driven energy conversion applications based on 3C-SiC - Sun, Jianwu; Jokubavicius, Valdas; Gao, Lu; Booker, Ian; Jansson, Mattias; Liu, Xinyu; Hofmann, Jan P; Hensen, Emiel J.M.; Linnarsson, M. K.; Wellmann, Peter; Ramiro, Inigo; Marti, Antonio; et al. (Materials Science Forum, 2016)
There is a strong and growing worldwide research on exploring renewable energy resources. Solar energy is the most abundant, inexhaustible and clean energy source, but there are profound material challenges to capture, convert and store solar energy. In this work, we explore 3C-SiC as an attractive material towards solar-driven energy conversion applications: (i) Boron doped 3C-SiC as candidate for an intermediate band photovoltaic material, and (ii) 3C-SiC as a photoelectrode for solar-driven water splitting. Absorption spectrum of boron doped 3C-SiC shows a deep energy level at 0.7 eV above the valence band edge. This indicates that boron doped 3C-SiC may be a good candidate as an intermediate band photovoltaic material, and that bulk like 3C-SiC can have sufficient quality to be a promising electrode for photoelectrochemical water splittin
Keywords: Cubic silicon carbide (3C-SiC); Photoelectrochemical (PEC) water splitting; Solar cell

Solar-NIRT: Identification of PV-module backsheets in the field with natural sunlight - Stroyuk, Oleksandr; Buerhop-Lutz, Claudia; Hauch, Jens; Peters, Ian Marius (Progress in Photovoltaics, 2021)
Reliable and durable solar power plants require PV modules with high-grade polymer encapsulants and backsheets (BSs). For performance analyses of PV installations fast, reliable and non-destructive methods for determining composition and degradation state of polymer components need to be developed. Here, we show that the structure of some common polymer BSs can be determined in the field in real time by analyzing near-infrared transmission (NIRT) spectra collected under illumination with natural sunlight. The potential of this “Solar-NIRT” method was probed by field measurements on a multi-MW PV power plant where four major BS types were identified by multispectral cross-sectional Raman imaging. Additionally, degradation of a particular BS type was found to result in distinct changes in NIRT spectra allowing the degraded BSs to be classified as a separate type. Principal component analysis (PCA) applied to a collection of 62 Solar-NIRT spectra allowed to create a map of five clusters, each corresponding to a particular BS type. The feasibility of using the PCA cluster map for the identification of unknown samples was shown on a test set of 13 different BSs. The Solar-NIRT is relatively fast, non-invasive, selective, can be upgraded to a non-contact regime making it a promising tool for high-throughput characterization.
CRIS-Team Scopus Importer:2021-10-08

Solar spectral conversion for improving the photosynthetic activity in algae reactors - Wondraczek, Lothar; Batentschuk, Miroslaw; Schmidt, Markus A.; Borchardt, Rudolf; Scheiner, Simon; Seemann, Benjamin; Schweizer, Peter; Brabec, Christoph (Nature Communications, 2013)
Sustainable biomass production is expected to be one of the major supporting pillars for future energy supply, as well as for renewable material provision. Algal beds represent an exciting resource for biomass/biofuel, fine chemicals and CO storage. Similar to other solar energy harvesting techniques, the efficiency of algal photosynthesis depends on the spectral overlap between solar irradiation and chloroplast absorption. Here we demonstrate that spectral conversion can be employed to significantly improve biomass growth and oxygen production rate in closed-cycle algae reactors. For this purpose, we adapt a photoluminescent phosphor of the type Ca SrEuS, which enables efficient conversion of the green part of the incoming spectrum into red light to better match the Q peak of chlorophyll b. Integration of a Ca SrEuS backlight converter into a flat panel algae reactor filled with Haematococcus pluvialis as a model species results in significantly increased photosynthetic activity and algae reproduction rate. © 2013 Macmillan Publishers Limited. All rights reserved.

Solubility and dissolution kinetics of GaN in supercritical ammonia in presence of ammonoacidic and ammonobasic mineralizers - Schimmel, Saskia; Koch, Martina; Macher, Philipp; Kimmel, Anna-Carina; Steigerwald, Thomas; Alt, Nicolas; Schlücker, Eberhard; Wellmann, Peter (Journal of Crystal Growth, 2017)
Solubility and dissolution kinetics of GaN are investigated, as they represent essential parameters for ammonothermal crystal growth of GaN. In situ X-ray imaging is applied to monitor the dissolving crystal. Both ammonoacidic and ammonobasic conditions are investigated. Compared to NH4F, the dissolution is generally much slower using NaN3 mineralizer, leading to a much longer time needed to establish a saturated solution. The solubility of GaN at 540 °C and 260 MPa in supercritical ammonia with a molar concentration of NaN3 of 0.72 mmol/ml is determined to be 0.15 ± 0.01 mol%. This suggest a severe refinement of raw gravimetric literature data also for alkali metal based mineralizers, as we reported previously for ammonium halide mineralizers. The order of magnitude is in good agreement with refined gravimetric solubility data (Griffiths et al., 2016). The apparent discrepancy between the literature and this work regarding the temperature range in which retrograde solubility occurs is discussed. A possible reason for the occurrence of retrograde solubility at high temperatures is described. The paper is complemented by a section pointing out and partially quantifying potential, reactor-material-dependent sources of errors.
Keywords: Solubility; Solvents; Ammonothermal crystal growth; Growth from solutions; Solvothermal crystal growth; Gallium compounds

Solubility and miscibility for diluted polymers and their extension to organic semiconductors - Perea Ospina, Jose Dario; Langner, Stefan; Ameri, Tayebeh; Brabec, Christoph (Encyclopedia of Physical Organic Chemistry, 6 Volume Set, Band 1, 2017)

Solubility Based Identification of Green Solvents for Small Molecule Organic Solar Cells - Burgues-Ceballos, Ignasi; Machui, Florian; Min, Jie; Ameri, Tayebeh; Voigt, Monika M.; Luponosov, Yuriy N.; Ponomarenko, Sergei A.; Lacharmoise, Paul D.; Campoy-Quiles, Mariano; Brabec, Christoph (Advanced Functional Materials, 2014)
Replacing halogenated solvents in the processing of organic solar cells by green solvents is a required step before the commercialization of this technology. With this purpose, some attempts have been made, although a general method is yet to be developed. Here, the potential of the Hansen solubility parameters (HSP) analysis for the design of green ink formulations for solution-processed active layer in bulk heterojunction photovoltaic devices based on small molecules is demonstrated. The motivation of moving towards organic small molecules stems from their lower molecular weight and more definite structure which makes them more likely to be dissolved in a wider variety of organic solvents. In the first step, the HSP of selected active materials are determined, namely, the star-shaped D-π-A tris[4-[5′′-(1,1-dicyanobut-1-en-2-yl)-2,2′-bithiophen-5-yl]pheny]amine N(Ph-2T-DCN-Et)3 small molecule and fullerene derivative [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM). Secondly, computer simulations based on HSP allow the prediction of suitable green solvents for this specific material system. The most promising green solvents, according to the simulations, are then used to fabricate solar cell devices using pristine solvents and two solvents mixtures. These devices show power conversion efficiencies around 3.6%, which are comparable to those obtained with halogenated solvents. This good performance is a result of the sufficient solubility achieved after a successful prediction of good (green) solvents.
Keywords: Hansen solubility parameters; ink formulations; non-halogenated solvents; organic photovoltaics; small molecule

Solubility, Miscibility, and the Impact on Solid-State Morphology - Brabec, Christoph; Machui, Florian (Wiley-VCH, 2013)
Keywords: Glass transition temperature; Miscibility; Organic semiconductors; Phase diagram; Solar cells; Solubility

Solution-coated barriers for organic electronics - Channa, Iftikhar Ahmed; Distler, Andreas; Brabec, Christoph; Egelhaaf, Hans-Joachim (Organic Flexible Electronics, 2021)
This chapter provides a review on solution processed barriers for flexible organic electronics. After elaborating on the necessity for encapsulation of organic devices by describing the degradation mechanisms caused by oxygen and water, the state of the art of vacuum-deposited barriers is briefly addressed as it presently defines the benchmark of barrier technology. Subsequently, the fundamentals of permeation of gases through barriers and the characterization methods for barrier performance are described. The main part of the chapter gives an overview of the material systems used for manufacturing solution-processed barriers. We start with the methods relying on reducing diffusion and solubility coefficients of oxygen and water in barrier films. Subsequently, barriers based on tortuosity and barriers based on covering substrates with layers of zero or very low permeability are described. Finally, the role of getters is elucidated. The chapter is concluded with highlighting some of the present challenges in the field of solution processed flexible barriers.<br
Keywords: Flexible barriers; flexible electronics; flexible packaging; organic photovoltaics; organic light emitting diodes; OLED; OPV; OFET; device lifetime; accelerated ageing

Solution-Growth Liquid-Phase Epitaxy of CsPbBr3 on NaCl by Optimizing the Substrate Dissolution - Elia, Jack; Levchuk, Ievgen; Hou, Yi; Matt, Gebhard; These, Albert; Zhao, Yicheng; Zhang, Jiyun; Forberich, Karen; Osvet, Andres; Götz, Klaus; Prihoda, Annemarie; Wu, Mingjian; et al. (Journal of Physical Chemistry C, 2023)
Since the earliest days of liquid-phase epitaxy (LPE) research, substrate stability has been a prerequisite for investigating nucleation and epitaxial growth. For flux- and melt-growth LPE, soluble substrates have always been viewed as problematic and difficult. However, solution-growth LPE transforms this disadvantage into a benefit by facilitating the creation of graded interfaces. In this study, we investigated the nucleation and growth of solution-grown LPE in the evaporation mode of soluble CsPbBr3 on freshly cleaved NaCl single-crystal substrates. Only two of the four main types of CsPbBr3 crystallization observed are epitaxial. The microscopic observation of composition gradients at the interface of CsPbBr3 grains and substrates reveals a promising opportunity to manipulate the lattice constant at the interface by simply controlling the temperature and concentration.
CRIS-Team Scopus Importer:2023-12-08

Solution Growth of Silicon Carbide Using the Vertical Bridgman Method - Fahlbusch, Lars; Wellmann, Peter (Crystal Research and Technology, 2018)
A solution growth process combined of vertical Bridgman and vertical gradient freeze in a metal free Si-C melt at growth temperatures of 2300 °C is developed. The influence of the growth parameters for different growth steps and of the surface polarity of the seed is investigated. The layers are evaluated by Raman spectroscopy, scanning electron microscopy and optical profilometry. The growth of high quality SiC layers with a diameter of 30 mm and a layer thickness up to 200 μm is achieved.<br
Keywords: High temperature growth; Solution growth; Silicon carbide; Vertical Bridgman

Solution-Processed Metallic Nanowire Electrodes as Indium Tin Oxide Replacement for Thin-Film Solar Cells - Krantz, Johannes; Richter, Moses; Spallek, Stefanie; Spiecker, Erdmann; Brabec, Christoph (Advanced Functional Materials, 2011)
Solution processed silver nanowire (Ag NW) films are introduced as transparent electrodes for thin-film solar cells. Ag NW electrodes were processed by doctor blade-coating on glass substrates at moderate temperatures (less than 100 degrees C). The morphological, optical, and electrical characteristics of these electrodes were investigated as a function of processing parameters. For solar-cell application, Ag NW electrodes with an average transparency of 90% between 450 and 800 nm and a sheet resistivity of 10 O per square were chosen. The performance of poly(3-hexylthiophen-2,5-diyl):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) solar cells on Ag NW electrodes was found to match the performance of otherwise identical cells on indium tin oxide. Overall, P3HT:PCBM solar cells with an efficiency of 2.5% on transparent Ag NW electrodes have been realized.
Keywords: silver nanowires; electrodes; organic electronics; indium tin oxide replacement; solar cells

Solution processed oxygen and moisture barrier based on glass flakes for encapsulation of organic (opto-) electronic devices - Channa, Iftikhar Ahmed; Distler, Andreas; Scharfe, Benedikt; Feroze, Sarmad; Forberich, Karen; Lipovsek, Benjamin; Brabec, Christoph; Egelhaaf, Hans-Joachim (Flexible and Printed Electronics, 2021)
The concept of transparent barriers against oxygen and water based on polymer films filled with glass flakes is presented. Barriers are prepared by casting polyvinyl butyral (PVB) films containing glass flakes of different aspect ratios (ARs) at different loadings to systematically study the effect of these parameters on barrier quality and optical transmission. It is found that the glass flakes are distributed homogeneously in the PVB film, with an almost perfect orientation of the long axes of the platelets parallel to the film surface. For glass flakes having an AR of 2000, barrier films with optical transmittance exceeding 85% and water vapor transmission rates of 0.14 g m(-2) d(-1) are obtained at a glass loading of 25 vol%. The haze of the glass flake filled PVB films, which is mainly due to surface roughness of the films according to optical simulations, is reduced by coating a smoothing layer on top. The barrier properties persist even after 20 000 cycles of bending at a radius of 3 cm. The lifetime of organic solar cells increases to beyond 1000 h under damp heat conditions as well as under constant illumination, when the devices are encapsulated with the PVB/glass flake composite films.
CRIS-Team WoS Importer:2021-06-25
Keywords: optical simulations; organic solar cell encapsulation; flexible barriers; glass flakes; polyvinyl butyral

Solution-Processed Parallel Tandem Polymer Solar Cells Using Silver Nanowires as Intermediate Electrode - Guo, Fei; Kubis, Peter; Li, Ning; Przybilla, Thomas; Matt, Gebhard; Stubhan, Tobias; Ameri, Tayebeh; Butz, Benjamin; Spiecker, Erdmann; Forberich, Karen; Brabec, Christoph (Acs Nano, 2014)
Tandem architecture is the most relevant concept to overcome the efficiency limit of single-junction photovoltaic solar cells. Series-connected tandem polymer solar cells (PSCs) have advanced rapidly during the past decade. In contrast, the development of parallel-connected tandem cells is lagging far behind due to the big challenge in establishing an efficient interlayer with high transparency and high in-plane conductivity. Here, we report all-solution fabrication of parallel tandem PSCs using silver nanowires as intermediate charge collecting electrode. Through a rational interface design, a robust interlayer is established, enabling the efficient extraction and transport of electrons from subcells. The resulting parallel tandem cells exhibit high fill factors of similar to 60% and enhanced current densities which are identical to the sum of the current densities of the subcells. These results suggest that solution-processed parallel tandem configuration provides an alternative avenue toward high performance photovoltaic devices.
Keywords: parallel-tandem; polymer solar cells; solution-processed; silver nanowires

Solution-processed tandem organic solar cells - Du, Xiaoyan; Li, Ning; Ding, Liming (Journal of Semiconductors, 2021)
CRIS-Team WoS Importer:2021-11-26

Solvent engineering of scalable deposited wide-bandgap perovskites for efficient monolithic perovskite-organic tandem solar cells - Tang, Yun; Zhang, Yuchao; Zhou, Xinming; Huang, Ting; Shen, Kai; Zhang, Kang Ning; Du, Xiaoyan; Shi, Tingting; Xiao, Xiudi; Li, Ning; Brabec, Christoph; Mai, Yaohua; et al. (Nano Energy, 2023)
High-quality wide-bandgap perovskite films are a key component in constructing efficient tandem solar cells. Although the efficiency of perovskite tandem devices advances rapidly in recent years, the majority of wide-bandgap perovskite films are deposited by laboratory spin-coating, which greatly hinders their commercial viability. Here, we first show that the widely-used binary solvents (DMF:DMSO) in spin-coating are incapable of producing qualified wide-bandgap perovskite films by scalable methods. It is identified that dense and uniform wide-bandgap thin films can be deposited from single-solvent NMP by blade-coating, which is mainly related to the well-controlled crystallization kinetics enabled by the formation of stable intermediate adduct. Along with a rational passivation by constructing a 2D/3D layered heterojunction, inverted perovskite devices with a bandgap of 1.8 eV deliver a champion efficiency of 18.92 %. On this basis, monolithic perovskite-organic tandem solar cells with an efficient and robust interconnection layer of “SnO2/Au/PEDOT:PSS” are fabricated, yielding a high efficiency of 22.25 % along with an impressive open-circuit voltage of 2.1 V. These results demonstrate an important step toward scalable fabrication of monolithic perovskite-organic tandem solar devices.
CRIS-Team Scopus Importer:2023-09-29
Keywords: Blade coating; Perovskite-organic; Solvent engineering; Tandem solar cells; Wide-bandgap

Spatial distribution of charge carrier temperature and -lifetime in semi-insulating InP:Fe, observed via photoluminescence spectroscopy - Waldmüller, S.; Lang, M.; Wellmann, Peter; Winnacker, Albrecht (Proceedings of 1994 IEEE 6th International Conference on Indium Phosphide and Related Materials (IPRM), 1994)
The authors determine the minority carrier lifetime (/spl tau/) in semi-insulating InP in an indirect way by analyzing the high energy tail of the photoluminescence spectrum and extracting a charge carrier temperature T/sub e/ from this data. T/sub e/ turns out to be directly related to /spl tau/, being small for large /spl tau/ and vice versa. It is shown that a) variations of the electron temperature can be observed in typical sample of LEC-grown InP:Fe, b) these variations can be analyzed in terms of charge carrier lifetimes, c) these temperature (and lifetime) variations can be correlated with the PL-intensity distribution and the Fe-distribution in the materia
Keywords: Charge carriers; Temperature distribution; Tellurium; Charge carrier processes; Electron emission; Photoluminescence; Semiconductor materials; Spontaneous emission; Indium phosphide; Phonons

Special Equipment for Ammonothermal Processes - Schlücker, Eberhard; Hertweck, Benjamin; Schimmel, Saskia; Wellmann, Peter (Ammonothermal Synthesis and Crystal Growth of Nitrides, 2021)
As the ammonothermal method often requires technically challenging conditions such as high temperature, high pressure and reaction media that are rather corrosive towards most metals (see Chap. 11), the further development of ammonothermal process equipment is of vital importance for tapping the full potential of the ammonothermal method. Suitable high-pressure/high-temperature autoclaves are therefore the basic requirement for a successful process. Ammonothermal syntheses are conventionally carried out in autoclaves, which do not allow monitoring of the physical and chemical processes during the experiments. Therefore, in situ measurement techniques at process conditions are crucial for obtaining a holistic understanding of ammonothermal processes. The following chapter presents optical cells for in situ monitoring enabling UV/Vis and Raman spectroscopy, X-ray imaging and X-ray diffraction as well as ultrasonic measurements. Additionally, special equipment like a rotatable feedthrough and a ceramic-crucible-based systems for minimization of corrosion and contamination are describe
Keywords: ammonothermal synthesis; crystal growth of nitrides; in situ monitoring; autoclave design; optical cells; rotatable feedthrough; ceramic crucible

Special Issue on Silicon Carbid CVD for Electronic Device Applications - Wellmann, Peter; Pons, Michel (Wiley-VCH, 2006)

Special section guest editorial: Solution-processable organic solar cells - Brabec, Christoph; Ameri, Tayebeh (Journal of Photonics for Energy, 2015)

Spectroscopic study of NE8 defect in synthetic diamond for optical thermometry - Sildos, I.; Loot, A.; Kiisk, V.; Puust, L.; Hizhnyakov, Vladimir; Yelisseyev, Alexander; Osvet, Andres; Vlasov, Igor (Diamond and Related Materials, 2017)
We carried out a laser spectroscopic investigation of high-pressure, high-temperature (HTHP) synthetic diamond containing NE8 defects. In the photoluminescence (PL) emission spectra the defects have a zero-phonon line (ZPL) at 794 nm. Under 730 nm excitation the width and position of the ZPL as well as the Debye-Waller factor showed systematic temperature dependences which were modelled in accordance of a modified model of impurity defects in solids. A strong dependence of the position of the 794 nm ZPL on temperature suggests that NE8-containing diamond could be suitable for sensitive optical thermometry above 200 K. Further, the PL in the NIR spectral range makes the diamond crystalline particles promising temperature sensors for biomedical applications
Keywords: Optical thermometry; Synthetic diamond; Optical defect

Spontaneous alloying of ultrasmall non-stoichiometric Ag-In-S and Cu-In-S quantum dots in aqueous colloidal solutions - Stroyuk, Oleksandr; Raievska, Oleksandra; Solonenko, Dmytro; Kupfer, Christian; Osvet, Andres; Batentschuk, Miroslaw; Brabec, Christoph; Zahn, Dietrich R. T. (RSC Advances, 2021)
The effect of spontaneous alloying of non-stoichiometric aqueous Ag-In-S (AIS) and Cu-In-S (CIS) quantum dots (QDs) stabilized by surface glutathione (GSH) complexes was observed spectroscopically due to the phenomenon of band bowing typical for the solid-solution Cu(Ag)-In-S (CAIS) QDs. The alloying was found to occur even at room temperature and can be accelerated by a thermal treatment of colloidal mixtures at around 90 °C with no appreciable differences in the average size observed between alloyed and original individual QDs. An equilibrium between QDs and molecular and clustered metal-GSH complexes, which can serve as “building material” for the new mixed CAIS QDs, during the spontaneous alloying is assumed to be responsible for this behavior of GSH-capped ternary QDs. The alloying effect is expected to be of a general character for different In-based ternary chalcogenides.
CRIS-Team Scopus Importer:2021-07-23

Spontaneously Self-Assembly of a 2D/3D Heterostructure Enhances the Efficiency and Stability in Printed Perovskite Solar Cells - Hu, Jinlong; Wang, Chuan; Qiu, Shudi; Zhao, Yicheng; Gu, Ening; Zeng, Linxiang; Yang, Yuzhao; Li, Chaohui; Liu, Xianhu; Forberich, Karen; Brabec, Christoph; Nazeeruddin, Mohammad Khaja; et al. (Advanced Energy Materials, 2020)
As perovskite solar cells (PSCs) are highly efficient, demonstration of high-performance printed devices becomes important. 2D/3D heterostructures have recently emerged as an attractive way to relieving the film inhomogeneity and instability in perovskite devices. In this work, a 2D/3D ensemble with 2D perovskites self-assembled atop 3D methylammonium lead triiodide (MAPbI3) via a one-step printing process is shown. A clean and flat interface is observed in the 2D/3D bilayer heterostructure for the first time. The 2D perovskite capping layer significantly suppresses nonradiative charge recombination, resulting in a marked increase in open-circuit voltage (VOC) of the devices by up to 100 mV. An ultrahigh VOC of 1.20 V is achieved for MAPbI3 PSCs, corresponding to 91% of the Shockley–Queisser limit. Moreover, notable enhancement in light, thermal, and moisture stability is obtained as a result of the protective barrier of the 2D perovskites. These results suggest a viable approach for scalable fabrication of highly efficient perovskite solar cells with enhanced environmental stability.
CRIS-Team Scopus Importer:2020-03-27
Keywords: 2D/3D heterojunctions; high efficiency; perovskite solar cells; self-assembly; stability

Spray-Coated Organic Photodetectors and Image Sensors with Silicon-Like Performance - Biele, Markus; Montenegro Benavides, Cindy; Hürdler, Judith; Tedde, Sandro F.; Brabec, Christoph; Schmidt, Oliver (Advanced Materials Technologies, 2018)
Solution-processed bulk heterojunction based organic photodiodes are ideal candidates for large-area light sensing. Here, spray-coated large-area organic photodiodes based on a novel polymer (Lisicon PV-D4650) with dark current densities down to 34 pA cm−2 and a maximum responsivity of ≈0.44 A W−1@660 nm under reverse bias conditions of −5 V are reported. These values are comparable to commercially available state-of-the-art solid-state photodetectors. Furthermore, cutoff frequencies of 50 kHz and a linear dynamic range exceeding eight orders of magnitude or ≥160 dB are achieved. The usage of 1,8-diiodooctane as processing additive for spray coating vastly reduces the surface roughness of spray-coated organic photodiodes which facilitates the preparation of large-area light sensors and image sensors. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhe
Keywords: surface roughness; responsivity; spray coating; OPD; imaging

Spray-Coated Silver Nanowires as Top Electrode Layer in Semitransparent P3HT:PCBM-Based Organic Solar Cell Devices - Krantz, Johannes; Stubhan, Tobias; Richter, Moses; Spallek, Stefanie; Litzov, Ivan; Matt, Gebhard; Spiecker, Erdmann; Brabec, Christoph (Advanced Functional Materials, 2013)
Silver nanowire (Ag NW) thin films are investigated as top electrodes in semitransparent inverted organic solar cells. The performance of semitransparent poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) organic solar cells with Ag NW top electrode layers is found to match very closely the performance of reference devices based on thermally evaporated, highly reflective metal silver top electrodes. The optical losses of the semitransparent electrodes are investigated in detail and analyzed in terms of transmission, scattering, and reflection losses. The impact on an external back reflector is shown to increase the light harvesting efficiency of optically thin devices. Further analysis of transparent devices under illumination from the indium tin oxide (ITO) backside and through the Ag NW front electrode open the possibility to gain deep insight into the vertical microstructure related devices performance. Overall, Ag NW top electrodes are established as a serious alternative to TCO based electrodes. Semitransparent devices with efficiencies of over = 2.0% are realized.
Keywords: silver nanowires; electrodes; semitransparent photovoltaic devices; organic electronics; spray deposition

Squeezing the Threshold of Metal-Halide Perovskite Micro-Crystal Lasers Grown by Solution Epitaxy - Zhou, Shuyu; Rehm, Viktor; Afify, Hany A.; Feng, Yufei; Korczak, Jędrzej; Szczerbakow, Andrzej; Story, Tomasz; Peng, Zijian; These, Albert; Barabash, Anastasia; Osvet, Andres; Brabec, Christoph; et al. (Advanced Functional Materials, 2024)
Metal halide perovskite semiconductors have demonstrated remarkable progress not only in photovoltaics and X-ray detection but also in laser technologies. Particularly appealing is the simplicity with which micro-crystallites can be epitaxially grown, thereby forming micro-resonators suitable for lasing. Here, the laser threshold is optimized by selecting excitation laser parameters and by improving material quality. The latter process is conducted for formamidinium lead tribromide, emitting in the green spectral range. Depending on the growth method and parameters, the sizes of the micro-resonators can be tuned between ≈3 and 23 micrometers. Under laser excitation systematically lower thresholds are observed for micro-resonators in the 4–7 micrometer size range, than for larger ones, irrespective of growth method. Among three optimized growth methods, epitaxial growth via antisolvent vapor-assisted crystallization exhibits the smallest threshold powers, indicating the highest material quality. This conclusion is supported by hyperspectral microscopic luminescence imaging and by transient photoluminescence. The best laser structures exhibit record threshold powers for epitaxially grown perovskites, indicating that the selected antisolvent vapor epitaxial growth holds great promises also for other perovskite materials.
CRIS-Team Scopus Importer:2024-05-10
Keywords: FAPbBr; lasing; micro-resonators; perovskites; solution epitaxy

Stability criteria for 4H-SiC bulk growth - Straubinger, Thomas; Bickermann, Matthias; Hofmann, Heinz-Dieter; Weingärtner, Roland; Wellmann, Peter; Winnacker, Albrecht (Materials Science Forum, 2001)
Types i and ii of polytype instabilities (6H/15R) were observed to be not stable and overgrown by 4H. Furthermore type i could be avoided by a seeding procedure with low supersaturation. No dependence on pressure or axial temperature gradient was noticed for the type ii polytype generation mechanism. Concerning the complete conversion to 6H, 4H stability showed no correlation with the argon pressure but we found a critical temperature for conversion, which depends on the axial temperature gradient. Far low axial T-gradients the critical temperature decrease
Keywords: 4H-SiC; Polytype; PVT

Stability of Organic Solar Cells: From Fullerene Derivatives to Non-fullerene Acceptors - Du, Xiaoyan; Guo, Jing; Min, Jie; Li, Ning (Organic Solar Cells: Materials Design, Technology and Commercialization, 2022)
The development of organic photovoltaic (OPV) technologies has reached a respective scientific level of understanding. The power conversion efficiency (PCE) of >18% has been demonstrated for lab-scale organic solar cells (OSCs), while large-scale organic solar modules (>200 cm 2) have achieved PCEs close to 12%. In order to continuously develop the OPV technologies toward commercialization, it is imperative to in-depth investigate the stability issues of OSCs under various conditions and to understand corresponding degradation mechanisms. The development of OSCs from fullerene derivatives to non-fullerene acceptors (NFAs) not only promotes the device performance to a significantly high level but also greatly changes the understanding of device stability, especially the microstructure stability of photoactive layers. In this book chapter, we first introduce the factors limiting the stability of OSCs, including extrinsic factors related to external stresses and intrinsic factors related to materials and devices. We summarize the stability evaluation protocols based on the test guidelines introduced by the International Electrotechnical Commission (IEC) and the International Summits on Organic PV Stability (ISOS). We focus our efforts on the development of stable OSCs based on different acceptors and summarize in detail the effective strategies to enhance the microstructure stability of OSCs. We hope that this work can arouse more attention in the community to the stability of OSCs and can contribute to the development of next-generation OSCs with excellent device performance as well as excellent operational stability, which is required for large-scale production and commercial applications.
CRIS-Team Scopus Importer:2024-12-16

Stabilization of aluminum doped zinc oxide nanoparticle suspensions and their application in organic solar cells - Wolf, N.; Stubhan, Tobias; Manara, J.; Dyakonov, Vladimir; Brabec, Christoph (Thin Solid Films, 2014)
Aluminum doped zinc oxide (AZO) nanoparticles were redispersed in isopropyl alcohol and stabilized with different stabilizers and mixtures of stabilizers that allow for electronically functional particles. The size of the redispersed nanoparticles was small enough to use these suspensions to build interfacial layers in inverted polymer-fullerene solar cells. The performance of these devices was found to depend on the stabilizer used in the nanoparticle suspension. The best performance was obtained with an AZO interfacial layer built with a 3,6,9-trioxadecanoic acid and polyvinylpyrrolidone stabilized nanoparticle suspension. (C) 2014 Elsevier B.V. All rights reserved.
Keywords: Aluminum doped zinc oxide; Nanoparticle suspensions; Interfacial layers; Inverted polymer-fullerene solar cells

Standardization as an Instrument to Accelerate the Development of Stable Emerging Photovoltaic Technologies—The IEC TS 62876-2-1:2018—Technical Specification for the Stability Testing of Photovoltaic Devices Enabled by Nanomaterials - Hauch, Jens; Brabec, Christoph; Fabricius, Norbert; Bergholz, Werner (Energy Technology, 2020)
For new photovoltaic (PV) technologies the improvement and quantification of stability is a significant challenge. Accelerated aging tests are usually applied to shorten development times. While many of these tests exist, there is no standard that can serve as a guideline for choosing relevant tests and applying them correctly to achieve comparability between results. With the IEC TS 62876-2-1:2018 for the first time, a standard has been developed which defines the most significant testing protocols for stability. This standard is designed especially for third-generation PV technologies that utilize nanomaterials but may be applied to any other new PV technologies as well. The standard defines the relevant stresses, recommends values for testing, defines seven standard tests, and provides reporting requirements for documentation. As a stability criterion the time t80, the time it takes for a measured efficiency of a device to reach 80% of the initial efficiency during the testing, is applied. A wide adoption of the tests outlined in the IEC TS 62876 significantly shortens development times and decreases the time to market for emerging PV technologies.
CRIS-Team Scopus Importer:2020-08-14
Keywords: nano-enabled photovoltaic devices; photovoltaics; stabilities; standards; technical specifications

Star-shaped D-π-A oligothiophenes with a tris(2-methoxyphenyl)amine core and alkyldicyanovinyl groups: synthesis and physical and photovoltaic properties - Luponosov, Yuriy N.; Min, Jie; Solodukhin, Alexander N.; Bakirov, Artem V.; Dmitryakov, Petr V.; Shcherbina, Maxim A.; Peregudova, Svetlana M.; Cherkaev, Georgiy V.; Chvalun, Sergei N.; Brabec, Christoph; Ponomarenko, Sergei A. (Journal of Materials Chemistry C, 2016)
Synthesis of a series of star-shaped oligomers having a novel electron donating tris(2-methoxyphenyl)amine (m-TPA) core, which is linked through a bithiophene or terthiophene extgreekp-bridge with electron-deficient alkyldicyanovinyl (alkyl-DCV) groups, is described. A comprehensive study of the oligomers revealed significant dependence of their physical properties, including absorption, molecular frontier energy levels, crystal packing, and melting and glass transition temperatures, upon the chemical structure. A comparison of their photophysical properties to the nearest analog having the common dicyanovinyl (DCV) groups demonstrated a number of benefits to use alkyl-DCV units for the design of donor–acceptor small molecules: higher solubility, increased electrochemical stability, better photovoltaic performance, and possibility to control the relative physical and photovoltaic properties by a simple adjustment of alkyl and extgreekp-bridge lengths. Modification of the well-known triphenylamine (TPA) core in the star-shaped oligomers by methoxy groups increases not only solubility, but also crystallinity of the oligomers, whereas their photovoltaic performance stays on a similar level as their analogs with a TPA core. The study demonstrates that these design strategies represent interesting and simple tools for the effective modulation of properties of star-shaped molecules.
EAM Import::2019-03-13
Keywords: Engineering controlled terms: Crystal structure; Glass transition; Molecules; Oligomers; Solubility Design strategies; Electrochemical stabilities; Electron-deficient; Electron-donating; Photophysical properties; Photovoltaic performance; Photovoltaic property; Star-shaped molecules Engineering main heading: Stars

Statistical Analysis of Infrared-Inspections of PV-Plants - Buerhop, Claudia; Pickel, Tobias; Scheuerpflug, Hans; Hauch, Jens; Camus, Christian; Brabec, Christoph (33rd European Photovoltaic Solar Energy Conference and Exhibition, 2017)
First statistical evaluation of IR-inspections of PV-plants reveals that 81% of the installed PV-plants show IR-abnormalities. More than 140 PV-plants with more than 200,000 PV-modules were inspected and evaluated statistically. Main IR-abnormalities or failures in modules and string installations are analyzed, respectively. The average failure rate for PV-modules is about 6% and for module strings approximately 1%. The differentiation based on the installation type reveals that small residential installations relatively seen show more defective modules than large field installations. A first estimation of the missed income by not detecting and maintaining major module and plant failures yield a missed income of about 100 Mio. EUR considering the PV-systems installed in Germany. IR-imaging is a valuable method to give fast and reliable information about the actual quality and failure rate in inspected PV-installations.
Keywords: Performance; IR Imaging; Statistics; Failure

Statistical overview of findings by IR-inspections of PV-plants - Buerhop, Claudia; Pickel, Tobias; Scheuerpflug, Hans; Camus, Christian; Hauch, Jens; Brabec, Christoph (Proceedings of SPIE - The International Society for Optical Engineering, 2016)
First statistical evaluation of IR-inspections of PV-plants reveals that 86% of the installed PV-plants show IR-Abnormalities. More than 120 PV-plants with more than 160,000 PV-modules were inspected and evaluated statistically. Main IR-Abnormalities or failures in modules and string installations are analyzed, respectively. The average failure rate for PV-modules is about 8% and for module strings approximately 4%. The differentiation between the installation locations reveals that small residential installation show relatively more defective modules than large field installations.-Therefore, IR-imaging is a valuable method to give fast and reliable information about the actual quality and failure rate in inspected PV-installations.
Keywords: Defects; Failure; IR-images; PV-modules; Statistics; Substrings

Status of 3C-SiC Growth and Device Technology - Wellmann, Peter; Schöler, Michael; Schuh, Philipp; Jennings, Mike; Li, Fan; Nipoti, Roberta; Severino, Andrea; Anzalone, Ruggero; Roccaforte, Fabrizio; Zimbone, Massimo; Via, Francesco La (wiley, 2021)
Since the early days of research in the field of the wide band gap semiconductor silicon carbide (SiC), the cubic polytype has been favorable because it exhibits the highest electron mobility. The electronic band gap and electric breakdown are slightly smaller than the hexagonal 4H-SiC. Therefore, the ideal operation range of power electronic devices based on 3C-SiC lies in the mid-voltage range of 400-600 V as it is used in the large application field of electric automotive applications. The current review presents a state-of-the-art overview over the complete processing change from materials growth to device processing.
CRIS-Team Scopus Importer:2024-12-16
Keywords: 3C-SiC bulk growth; 3C-SiC device processing; 3C-SiC MOSFET; 3C-SiC thin films; cubic silicon carbide

Status of SiC bulk growth processes - Chaussende, D.; Wellmann, Peter; Pons, Michel (Journal of Physics D-Applied Physics, 2007)
The present paper gives an overview of the different routes to grow SiC single crystals. The focus is put on the new emerging processes compared with the well established ones. A review of the process engineering modelling is given. Finally, some selected results are pointed out as they should be considered for the future development of SiC material.
Keywords: Silicon carbide (SiC); crystal growth; vapour phase growth; reactor concepts; liquid phase growth; process modelling; doping; in-situ x-ray imaging

Step-flow growth of fluorescent 4H-SiC layers on 4 degree off-axis substrates - Schimmel, Saskia; Kaiser, Michl; Hens, Philip; Jokubavicius, Valdas; Liljedahl, Rickard; Sun, Jianwu; Yakimova, Rositsa; Ou, Yiyu; Ou, Haiyan; Linnarsson, Margareta K.; Wellmann, Peter; Syväjärvi, Mikael (Materials Science Forum, 2013)
Homoepitaxial layers of fluorescent 4H-SiC were grown on 4 degree off-axis substrates by sublimation epitaxy. Luminescence in the green spectral range was obtained by co-doping with nitrogen and boron utilizing donor-acceptor pair luminescence. This concept opens possibilities to explore green light emitting diodes using a new materials platfor
Keywords: fluorescent silicon carbide; sublimation epitaxy; co-doping; donor-acceptor pair luminescence; light conversion

Steric Engineering Enables Efficient and Photostable Wide-Bandgap Perovskites for All-Perovskite Tandem Solar Cells - Wen, Jin; Zhao, Yicheng; Liu, Zhou; Gao, Han; Lin, Renxing; Wan, Sushu; Ji, Chenglong; Xiao, Ke; Gao, Yuan; Tian, Yuxi; Xie, Jin; Brabec, Christoph; et al. (Advanced Materials, 2022)
Wide-bandgap (WBG, ≈1.8 eV) perovskite is a crucial component to pair with narrow-bandgap perovskite in low-cost monolithic all-perovskite tandem solar cells. However, the stability and efficiency of WBG perovskite solar cells (PSCs) are constrained by the light-induced halide segregation and by the large photovoltage deficit. Here, a steric engineering to obtain high-quality and photostable WBG perovskites (≈1.8 eV) suitable for all-perovskite tandems is reported. By alloying dimethylammonium and chloride into the mixed-cation mixed-halide perovskites, wide bandgaps are obtained with much lower bromide contents while the lattice strain and trap densities are simultaneously minimized. The WBG PSCs exhibit considerably improved performance and photostability, retaining >90% of their initial efficiencies after 1000 h of operation at maximum power point. With the triple-cation/triple-halide WBG perovskites enabled by steric engineering, a stabilized power conversion efficiency of 26.0% in all-perovskite tandem solar cells is further obtained. The strategy provides an avenue to fabricate efficient and stable WBG subcells for multijunction photovoltaic devices.
CRIS-Team Scopus Importer:2022-06-03
Keywords: all-perovskite tandem solar cells; lattice strain; light-induced halide segregation; steric engineering; wide-bandgap perovskite solar cells

Strain-activated light-induced halide segregation in mixed-halide perovskite solids - Zhao, Yicheng; Miao, Peng; Elia, Jack; Hu, Huiying; Wang, Xiaoxia; Heumüller, Thomas; Hou, Yi; Matt, Gebhard; Osvet, Andres; Chen, Yu-Ting; Tarragó, Mariona; de Ligny, Dominique; et al. (Nature Communications, 2020)
Light-induced halide segregation limits the bandgap tunability of mixed-halide perovskites for tandem photovoltaics. Here we report that light-induced halide segregation is strain-activated in MAPb(I1−xBrx)3 with Br concentration below approximately 50%, while it is intrinsic for Br concentration over approximately 50%. Free-standing single crystals of CH3NH3Pb(I0.65Br0.35)3 (35%Br) do not show halide segregation until uniaxial pressure is applied. Besides, 35%Br single crystals grown on lattice-mismatched substrates (e.g. single-crystal CaF2) show inhomogeneous segregation due to heterogenous strain distribution. Through scanning probe microscopy, the above findings are successfully translated to polycrystalline thin films. For 35%Br thin films, halide segregation selectively occurs at grain boundaries due to localized strain at the boundaries; yet for 65%Br films, halide segregation occurs in the whole layer. We close by demonstrating that only the strain-activated halide segregation (35%Br/45%Br thin films) could be suppressed if the strain is properly released via additives (e.g. KI) or ideal substrates (e.g. SiO2).<br

Strain-Modulated Charge Transport in Flexible PbS Nanocrystal Field-Effect Transistors - Nugraha, Mohamad Insan; Matsui, Hiroyuki; Watanabe, Shun; Kubo, Takayoshi; Häusermann, Roger; Bisri, Satria Zulkarnaen; Sytnyk, Mykhailo; Heiß, Wolfgang; Loi, Maria Antonietta; Takeya, Jun; Heiß, Wolfgang (Advanced Electronic Materials, 2017)
Keywords: colloidal nanocrystals; flexible field-effect transistors; ion gel; strain; nanocrystal transistors

Structural defects in aluminium nitride bulk crystals visualized by cathodoluminescence maps - Bickermann, Matthias; Schimmel, Saskia; Epelbaum, Boris; Filip, Octavian; Heimann, Paul; Nagata, Shunro; Winnacker, Albrecht (Physica Status Solidi (C) Current Topics in Solid State Physics, 2011)
Structural defects in aluminium nitride (AlN) get visible in panchromatic cathodoluminescence (CL) maps as luminescence at 340 nm and 630 nm is locally enhanced. Low-angle grain boundaries (LAGBs) and dislocations can be detected as long as they are sufficiently decorated and the defect-related contrast is higher than local variations in background CL intensity. We applied the method to c-plane and a-plane cuts of one of our off-oriented grown AlN crystals and describe occurrence, routes, and dissolution into dislocation bunches of LAGBs. We found that the vast majority of LAGBs are uneven a-planes which extend in a preferential m-as well as in c-direction. As a consequence, their density decreases only slightly during growth. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Keywords: AlN; growth from vapour; low angle grain boundaries; mosaicity; panchromatic cathodoluminescence mapping

Structural defects in SiC crystals investigated by high energy x-ray diffraction - Weißer, Matthias; Seitz, Christoph; Wellmann, Peter; Hock, Rainer; Magerl, Andreas (Materials Science Forum, 2004)
High energy x-ray diffraction (up to 300 keV) has been used to analyse structural defects in an as grown SiC boule with a diameter of 55 nun, a thickness of 20 mm and in a 2 inch wafer. The crystals are 6H SiC grown by PVT method. In the wafer numerous grains can be identified and localised with a mosaicity in the order of 0.05degrees, whereas the whole wafer shows a mosaic spread of around 0.1degrees. The bulk crystal shows a pronounced domain structure and a bending in the lattice plane orientation. The local reflection broadening is between 0.2degrees and 2degrees, while the tilts of the lattice planes over the entire wafer are between 2 and 6degrees (2theta-values
Keywords: Domain Structure; High Energy Diffraction; Structural Defects; X-Ray Diffraction (XRD)

Structural fluctuations cause spin-split states in tetragonal (CH₃NH₃)PbI₃ as evidenced by the circular photogalvanic effect - Niesner, Daniel; Hauck, Martin; Shrestha, Shreetu; Levchuk, Ievgen; Matt, Gebhard; Osvet, Andres; Batentschuk, Miroslaw; Brabec, Christoph; Weber, Heiko B.; Fauster, Thomas (Proceedings of the National Academy of Sciences of the United States of America, 2018)
Lead halide perovskites are used in thin-film solar cells, which owe their high efficiency to the long lifetimes of photocarriers. Various calculations find that a dynamical Rashba effect could significantly contribute to these long lifetimes. This effect is predicted to cause a spin splitting of the electronic bands of inversion-symmetric crystalline materials at finite temperatures, resulting in a slightly indirect band gap. Direct experimental evidence of the existence or the strength of the spin splitting is lacking. Here, we resonantly excite photocurrents in single crystalline (CH3NH3)PbI3 with circularly polarized light to clarify the existence of spin splittings in the band structure. We observe a circular photogalvanic effect, i.e., the photocurrent depends on the light helicity, in both orthorhombic and tetragonal (CH3NH3)PbI3. At room temperature, the effect peaks for excitation photon energies ΔE=110 meV below the direct optical band gap. Temperature-dependent measurements reveal a sign change of the effect at the orthorhombic extendashtetragonal phase transition, indicating different microscopic origins in the two phases. Within the tetragonal phase, both ΔE and the amplitude of the circular photogalvanic effect increase with temperature. Our findings support a dynamical Rashba effect in this phase, i.e., a spin splitting caused by thermally induced structural fluctuations which break inversion symmetr
Keywords: organic–inorganic perovskite; lead halide perovskite; circular photogalvanic effect; dynamical Rashba; Rashba effect

Structural, luminescence and photoconversion properties of Lu3Al5O12:Ce single crystalline film phosphors for WLED application - Markovskyi, Anton; Gorbenko, Vitalii; Yokosawa, Tadahiro; Will, Johannes; Spiecker, Erdmann; Batentschuk, Miroslaw; Elia, Jack; Fedorov, Alexander; Pakuła, Michał; Kaczmarek, Mariusz; Zorenko, Yuriy (Journal of Alloys and Compounds, 2022)
This work focuses on the detailed investigation of structural, luminescence and photoconversion properties of Ce doped Lu3Al5O12:Ce (LuAG:Ce) single crystalline films (SCFs) grown using the Liquid Phase Epitaxy (LPE) method onto Y3Al5O12 (YAG) single crystal substrates as promoting converting film material for high-power WLED. The structure and chemical composition were analyzed using X-ray diffraction (XRD) and High-Resolution Scanning Transmission Electron Microscopy (HR-STEM). HR-STEM analysis and composition analysis revealed an interface with high structural quality including the formation of a transition layer with a 6 nm thickness between LuAG:Ce SCF and YAG substrate. The composition of this layer changes smoothly from YAG substrate towards LuAG:Ce SCF, and after equalizing the SCF/substrate misfit, stable LuAG:Ce film growth is observed. The optical characterization of LuAG:Ce films were performed using absorbance, cathodoluminescence and photoluminescence emission/excitation spectra and photoluminescence decay lifetime, as well as photoconversion measurements under blue, LED excitation. The corresponding color coordinates, color temperatures, color rendering index and luminous efficacy of white light sources based on blue LEDs and LuAG:Ce film converters with thicknesses in the 19–160 nm range were estimated and best characteristics are achieved for the 92 µm thick sample.
CRIS-Team Scopus Importer:2022-10-21
Keywords: Ce; Liquid phase epitaxy; Lu; Planar-chip-level conversion; Single crystalline films; White LED

Structure and linkage assessment of T-shaped Pyrrolidine[60]Fullerene- and Isoxazoline[60]Fullerene-BODIPY-triarylamine hybrids - Rocha-Ortiz, Juan S.; Montalvo-Acosta, Joel José; He, Yakun; Insuasty, Alberto; Hirsch, Andreas; Brabec, Christoph; Ortiz, Alejandro (Dyes and Pigments, 2023)
Eight novel C60-BODIPY-Triarylamine electroactive triads have been synthesized and characterized. Using pyrrolidine (PIR and BDPF series) and isoxazoline (ISO series) as linkers between the fullerene and the BODIPY-Triarylamine (-TAA) system, the effect of these linkers along with different functionalization on the TAA on the electronic properties were studied. Moreover, their photophysical and electrochemical properties were investigated by comparing them to the reference substances BDP, 10a, 10b, and C60. All C60-BODIPY-TAA derivatives absorb visible light strongly in a range between 535 and 563 nm, and photoexcitation of the BODIPY unit causes photo-induced electron transfer, producing the corresponding charge-separated species, which was confirmed by solvatochromic effects on fluorescence measurements. The direction of charge transfer was also revealed by their redox potentials. A better electron affinity was observed for the ISO series when compared with PIR and BDPF. Thermogravimetric analysis showed that the pyrrolidine derivatives are more stable than their isoxazoline analogs and the insertion of alkoxy units in the triads triggers a better thermal endurance in the studied compounds.
CRIS-Team Scopus Importer:2023-06-30
Keywords: BODIPY dyes; Electron transfer; Isoxazoline[60]Fullerene; Pyrrolidine[60]Fullerene; Triarylamines

Study of boron incorporation during PVT growth of p-type SiC crystals - Bickermann, Matthias; Hofmann, Heinz-Dieter; Rasp, M.; Straubinger, Thomas; Weingärtner, Roland; Wellmann, Peter; Winnacker, Albrecht (Materials Science Forum, 2001)
The incorporation of the acceptor boron during vapor growth (PVT) of 6H-SiC bulk crystals has been studied. The chemical segregation coefficient of boron (ratio between B content of the grown crystal and of the source) has been determined to be 0.4 +/-0.1 for a wide range of B concentrations in tie starting material (0.1-300 ppm wt). For reference purposes the impurity concentrations in nominally undoped SiC crystals have been analyzed. Whereas both source and SiC crystals exhibit a high purity in regard to p-type (Al, B) and deep level (V, Ti) impurities, a considerable amount of residual nitrogen was detected resulting in carrier concentrations n = 1X10(16) to 1.5X10(17) cm(-3). Carrier concentrations in the p-type B doped crystals were found to range from 2X10(14) to 2X10(16) cm(-3) for starting B concentrations between 3 to 300 ppm wt. Axial nonuniformities, i.e. carrier concentration in SiC:B increases with crystal length, depend on the compensation ratio. At higher B content the homogeneity improves. Compared with segregation in Al doped SiC, results indicate that SiC:B powder acts as infinite, SiC:Al powder as finite dopant source. The lateral distribution of carrier concentration in SiC:B crystals (wafer mapping) has been measured showing a good homogeneity of electrical propertie
Keywords: Aluminum Doping; Boron Doping; Bulk Growth; Dopant Homogeneity

Sub-bandgap photon harvesting for organic solar cells via integrating up-conversion nanophosphors - Chen, Wei; Hou, Yi; Osvet, Andres; Guo, Fei; Kubis, Peter; Batentschuk, Miroslaw; Winter, Benjamin; Spiecker, Erdmann; Forberich, Karen; Brabec, Christoph (Organic Electronics, 2015)
Lanthanide-doped up-conversion nanophosphors were employed as up-conversion converters (UC-converters) combined with organic solar cells (OSCs). The optical properties of the external up-conversion layers were investigated, and the optimized layers were laminated with OSCs. Strong photocurrents were observed when OSCs with an UC converter were illuminated by a NIR laser. An improvement of photocurrent and efficiency were also observed under AM 1.5 G sun irradiation. Our investigations show a proof-of-concept that organic solar cells could utilize sub-bandgap photons via integrating up-conversion nanophosphors, which provide us a promising approach to exceed the efficiency limit of single junction organic solar cells.
Keywords: IR light harvesting; Nanophosphors; Organic photovoltaics; Up-conversion

Sublimation growth of bulk 3C-SiC using 3C-SiC-on-Si (1 0 0) seeding layers - Schuh, Philipp; Schöler, Michael; Wilhelm, Martin; Syväjärvi, Mikael; Litrico, G.; La Via, F.; Mauceri, M.; Wellmann, Peter (Journal of Crystal Growth, 2017)
We have developed a transfer process of 3C-SiC-on-Si (1 0 0) seeding layers grown by chemical vapor deposition onto a poly- or single-crystalline SiC carrier. Applying subsequent sublimation growth of SiC in [1 0 0] direction resulting in large area crystals (up to ≈11 cm2) with a thickness of up to approximately 850 <g fill="currentColor" stroke="currentColor" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><g><g><use xlink:href="http://www.sciencedirect.com/science/article/pii/S0022024817305377?via%3Dihub#MJMATHI-3BC"></use></g></g></g> m. Raman spectroscopy, Laue X-ray diffraction and electron-backscattering-diffraction revealed a high material quality in terms of single-crystallinity without secondary polytype inclusions, antiphase boundaries or double positioning grain boundaries. Defects in the bulk grown 3C-SiC, like protrusions with surrounding stressed areas, stem from the epitaxial seeding layer. The presented concept using 3C-SiC-on-Si seeding layers reveals a path for the growth of bulk 3C-SiC crystals.
Keywords: 3C-SiC; Quasi-bulk; Sublimation epitaxy; DPB free; Single crystalline; Stacking faults

Sublimation growth of thick freestanding 3C-SiC using CVD-templates on silicon as seeds - Hens, Philip; Jokubavicius, V.; Liljedahl, R.; Wagner, G.; Yakimova, R.; Wellmann, Peter; Syväjärvi, Mikael (Materials Letters, 2012)
Cubic silicon carbide is a promising material for medium power electronics operating at high frequencies and for the subsequent growth of gallium nitride for more efficient light emitting diodes. We present a new approach to produce freestanding cubic silicon carbide (3C-SiC) with the ability to obtain good crystalline quality regarding increased domain size and reduced defect density. This would pave the way to achieve substrates of 3C-SiC so that the applications of cubic silicon carbide material having selectively (111) or (001) oriented surfaces can be explored. Our method is based on the combination of the chemical vapor deposition method and the fast sublimation growth process. Thin layers of cubic silicon carbide grown heteroepitaxially on silicon substrates are for the first time used for a subsequent sublimation growth step to increase layer thicknesses. We have been able to realize growth of freestanding (001) oriented 3C-SiC substrates using growth rates around 120 mu m/h and diameters of more than 10 mm. The structural quality from XRD rocking curve measurements of (001) oriented layers shows good FWHM values down to 78 arcsec measured over an area of 1 x 2 mm(2), which is a quality improvement of 2-3 times compared with other methods like CVD. (C) 2011 Elsevier B.V. All rights reserved.
Keywords: Crystal growth; Defects; Physical vapor deposition; Semiconductors; Epitaxial growth; Thick films

Sublimations-Kristallzüchtung von Siliziumkarbid: Visualisierung und Modellbildung, Habilitationsschrift Universität Erlangen-Nürnberg - Wellmann, Peter (Shaker Verlag, 2001)

Sulfo-selenization of metallic thin films of Cu, In and Cu-In - Hölzing, Astrid; Schurr, R.; Schäfer, Horst; Jaeger, A.; Jost, S.; Palm, J.; Deseler, Klaus; Wellmann, Peter; Hock, Rainer (Thin Solid Films, 2009)
The affinity of the metals Cu and In is higher to sulfur. A crystallisation of mixed sulfo-selenides of Cu, In and Cu-In due to exchange reactions between S and Se is observed. Within the Cu-Se-S subsystem a wider solid solution range of S and Se is apparent as compared to the In-Se-S system. The reactions during the chalcopyrite crystallisation for chalcogen ratio [S]:[Se]=1:1 are similar to those of the pure sulfur system at least within the In-Se-S subsystem. (C) 2008 Elsevier B.V. All rights reserved.
Keywords: CuIn(S; Se)2; Chalcopyrite; Thin films; Real-time X-ray diffraction

Superior Performance of V2O5 as Hole Selective Contact over other Transition Metal Oxides in Silicon Heterojunction Solar Cells - Almora Rodriguez, Osbel; Gerling, Luis Guillermo; Voz, Cristóval; Alcubilla, Ramón; Puigdollers, Joaquim; Garcia-Belmonte, Germà (Solar Energy Materials and Solar Cells, 2017)
Transition metal oxides (TMOs) have recently been proved to efficiently serve as hole-selective contacts in crystalline silicon (c-Si) heterojunction solar cells. In the present work, two TMO/c-Si heterojunctions are explored using MoO3 (reference) and V2O5 as to alternative candidate. It has been found that V2O5 devices present larger (16% improvement) power conversion efficiency mainly due to their higher open-circuit voltage. While V2O5 / c-Si devices with textured front surfaces also have short-circuit currents, it is also known that flat solar cell architectures allow for the V2O5/n-Si interface, giving significant carrier lifetimes of 200 μs (equivalent to a surface recombination velocity of Seff 140 cm s-1) as derived from impedance analysis. As a consequence, a significant open-circuit voltage of 662 mV is achieved. It is found that, at the TMO/c-Si contact, a TMO work function enhancement ΔΦTMO occurs during the heterojunction formation with the consequent dipole layer enlargement Δ'= Δ + ΔΦTMO. TMO/c-Si contact energetics, carrier transport across the interface and surface TMO / c-Si heterojunctions.<br
Keywords: Transition metal oxides; Silicon solar cells; Impedance spectroscopy; Passivation; Minority carrier lifetime

Suppressing Nonradiative Losses in Wide-Band-Gap Perovskites Affords Efficient and Printable All-Perovskite Tandem Solar Cells with a Metal-Free Charge Recombination Layer - Zhou, Xinming; Lai, Hongwei; Huang, Ting; Chen, Chaoran; Xu, Zhenhua; Yang, Yuzhao; Wu, Shaohang; Xiao, Xiudi; Chen, Lang; Brabec, Christoph; Mai, Yaohua; Guo, Fei (ACS Energy Letters, 2023)
Although the efficiencies of all-perovskite tandem solar cells have surpassed 26%, further advancement of device performance is constrained by the large photovoltage deficit in wide-band-gap perovskite subcells. Meanwhile, state-of-the-art charge recombination layers incorporate an additional thin metal film (Au or Ag), which not only complexes device fabrication but induces parasitic optical losses. Here, we first fabricate efficient wide-band-gap perovskite solar cells (PSCs) with by suppressing nonradiative losses both in bulk material and at interface. The prepared PSCs with a band gap of 1.71 eV yield an impressive open-circuit voltage (VOC) of 1.27 V, giving a small VOC deficit of 0.44 V and an efficiency of 20.8%. We then fabricate monolithic all-printed perovskite tandem devices by constructing a metal-free recombination layer, which yields an efficiency of 23.65% and a high VOC of 2.05 V. This work offers a simple yet effective charge recombination architecture for advancing the performance of all-perovskite tandem devices.
CRIS-Team Scopus Importer:2023-02-03

Suppressing Nonradiative Recombination in Lead-Tin Perovskite Solar Cells through Bulk and Surface Passivation to Reduce Open Circuit Voltage Losses - Zhang, Kaicheng; Späth, Andreas; Almora, Osbel; Le Corre, Vincent Marc; Wortmann, Jonas; Zhang, Jiyun; Xie, Zhiqiang; Barabash, Anastasia; Hammer, Maria; Heumüller, Thomas; Min, Jie; Fink, Rainer; et al. (ACS Energy Letters, 2022)
Lead-Tin perovskite solar cells (Pb/Sn PSCs) are limited by the intrinsic instability of Sn(II), which tends to oxidize forming Sn vacancies in perovskite films. Herein, a Lewis base β-guanidinopropionic acid (GUA) and hydrazinium iodide (HAI) are introduced to effectively passivate the perovskite bulk and surface, respectively. The synergistic approach leads to Pb/Sn PSCs with a promising power conversion efficiency of 20.5% owing to the significantly reduced nonradiative recombination and voltage losses. As a result, the VOC × FF product of PSCs is significantly improved, which is among the highest values documented in the literature, being favorable for perovskite-based tandem applications. Additionally, the strategy demonstrated in this work could also improve the stability of PSCs by enhancing the chemical robustness of the perovskite layer. These results emphasize the significance of bulk and surface passivation in the development of efficient and stable PSCs based on Pb/Sn perovskites.
CRIS-Team Scopus Importer:2022-09-30

Suppressing photooxidation of conjugated polymers and their blends with fullerenes through nickel chelates - Salvador, Michael; Gasparini, Nicola; Perea, Jose Dario; Paleti, Harish; Distler, Andreas; Inasaridze, Liana N.; Troshin, Pavel A.; Luer, Larry; Egelhaaf, Hans-Joachim; Brabec, Christoph (Energy and Environmental Science, 2017)
Conjugated polymer semiconductors offer unique advantages over conventional semiconductors but tend to suffer from electro-optic performance roll-off, mainly due to reduced photofastness. Here, we demonstrate that the commodity nickel chelate nickel(ii) dibutyldithiocarbamate, Ni(dtc)2, effectively inhibits photooxidation across a wide range of prototypical π-conjugated polymer semiconductors and blends. The addition of 2-10 wt% of Ni(dtc)2 increases the resilience of otherwise quickly photobleaching semiconducting thin films, even in the presence of detrimental, radical forming processing additives. Using electron spin resonance spectroscopy and sensitive oxygen probes, we found that Ni(dtc)2 acts as a broadband stabilizer that inhibits both the formation of reactive radicals and singlet oxygen. The mechanism of stabilization is of sacrificial nature, but contains non-sacrificial contributions in polymers where singlet oxygen is a key driver of photooxidation. Ultrafast pump-probe spectroscopy reveals quenching of triplet excited states as the central mechanism of non-sacrificial stabilization. When introduced into the active layer of organic photovoltaic devices, Ni(dtc)2 retards the short circuit current loss in air without affecting the sensitive morphology of bulk heterojunctions and without major sacrifices in semiconductor properties. Antioxidants based on nickel complexes thus constitute functional stabilizers for elucidating degradation mechanisms in organic semiconductors and represent a cost-effective route toward organic electronic appliances with extended longevity. © 2017 The Royal Society of Chemistry.
Keywords: Engineering controlled terms: ChelationCost effectivenessDegradationElectron spin resonance spectroscopyHeterojunctionsMagnetic momentsNickelOxygenPhotobleachingPhotooxidationPolymer blendsProbesSemiconducting filmsSemiconductor devicesSpectroscopyStabilization Compendex keywords Degradation mechanismElectro-optic performanceOrganic electronicsOrganic photovoltaic devicesPolymer semiconductorsSemiconducting thin filmsSemiconductor propertiesUltrafast pump-probe spectroscopy Engineering main heading: Conjugated polymers

Suppressing photo-oxidation of non-fullerene acceptors and their blends in organic solar cells by exploring material design and employing friendly stabilizers - Guo, Jing; Wu, Yao; Sun, Rui; Wang, Wei; Guo, Jie; Wu, Qiang; Tang, Xiaofeng; Sun, Chenkai; Luo, Zhenghui; Chang, Kai; Zhang, Zhuohan; Yuan, Jun; et al. (Journal of Materials Chemistry A, 2019)
In addition to a high power conversion efficiency, ambient stability is another impact factor for the successful commercialization of organic solar cells (OSCs). Understanding the role of photovoltaic materials is the key to address this challenge, but no such studies have been systematically performed on non-fullerene acceptors (NFAs). In this work, we firstly investigate the role of NFA photo-oxidation in device degradation. Relevant investigation of physical dynamics underlines the effects on the device performance for NFA photo-oxidation acting as trap states in exposed blends. In addition, taking ITIC as an example, we shed some light on the possible mechanisms of NFA photo-oxidation, which cannot be eliminated by relevant strategies and principles of material design. These results drive us to further investigate the photobleaching rates of thirty-three NFAs, including fused-ring electron acceptors and perylene diimide acceptor derivatives. Surprisingly, most of them show a higher optical density loss as compared to their fullerene-based counterparts. In view of relevant comparative analysis in the Discussion section, we further propose some design strategies to improve the photo-oxidation stability of NFAs. More importantly, we also find a stabilizer (namely nickel chelate S6) that can effectively suppress the photo-oxidation of NFAs and their blends and thus improve the ambient stability of OSCs.
CRIS-Team Scopus Importer:2019-11-19

Suppressing the Surface Recombination and Tuning the Open-Circuit Voltage of Polymer/Fullerene Solar Cells by Implementing an Aggregative Ternary Compound - Galli, Diana; Gasparini, Nicola; Forster, Michael; Eckert, Anika; Widling, Christian; Killian, Manuela; Avgeropoulos, Apostolos; Gregoriou, Vasilis G.; Scherf, Ullrich; Chochos, Christos L.; Brabec, Christoph; Ameri, Tayebeh (ACS Applied Materials and Interfaces, 2018)
In this work, we present a novel small molecule based on dithienylthienothiadiazole units (named SM1) acting as an efficient component in ternary blend organic solar cells to modify the hole extraction at the interface. Our findings show that the SM1 suppresses the surface recombination and enhances the open-circuit voltage (Voc). By introducing SM1 in a host system composed of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), we obtained Voc values of up to 0.75 V and fill factors larger than 70% for the ternary blends. As a consequence, the power conversion efficiency is improved by about 30% compared to P3HT:PCBM binary devices. Interestingly, external quantum efficiency and absorption spectra in the near-infrared region do not show any contribution of SM1 in dried films. Instead, the addition of the small molecule improves the Voc by reducing the surface recombination losses. To shed light on the recombination processes, we carried out Fourier-transform photocurrent spectroscopy and impedance spectroscopy measurements. This work shows that the ternary concept can also have functionalities other than photosensitization and can even act as a morphology-directing agent or an interface modifie
Keywords: open-circuit voltages; recombination losses; ternary organic solar cells; sensitizers; small molecules

Suppression of Hysteresis Effects in Organohalide Perovskite Solar Cells - Hou, Yi; Scheiner, Simon; Tang, Xiaofeng; Gasparini, Nicola; Richter, Moses; Li, Ning; Schweizer, Peter; Chen, Shi; Chen, Haiwei; Ramírez Quiroz, César Omar; Du, Xiaoyan; Matt, Gebhard; et al. (Advanced Materials Interfaces, 2017)
Thin-film solar cell based on hybrid perovskites shows excellent light-to-power conversion efficiencies exceeding 22%. However, the mixed ionic-electronic semiconductor hybrid perovskite exhibits many unusual properties such as slow photocurrent instabilities, hysteresis behavior, and low-frequency giant capacitance, which still question us so far. This study presents a direct surface functionalization of transparent conductive oxide electrode with an ultrathin ≈2 nm thick phosphonic acid based mixed C60/organic self-assembled monolayer (SAM) that significantly reduces hysteresis. Moreover, due to the strong phosphonates bonds with indium tin oxide (ITO) substrates, the SAM/ITO substrates also exhibit an excellent recyclability merit from the perspective of cost effectiveness. Impedance studies find the fingerprint of an ion-based diffusion process in the millisecond to second regime for TiO2-based devices, which, however, is not observed for SAM-based devices at these low frequencies. It is experimentally demonstrated that ion migration can be considerably suppressed by carefully engineering SAM interfaces, which allows effectively suppressing hysteresis and unstable diode behavior in the frequency regime between ≈1 and 100 Hz. It is suggested that a reduced density of ionic defects in combination with the absence of charge carrier accumulation at the interface is the main physical origin for the reduced hysteresis.

Suppression of phase segregation in wide-bandgap perovskites with thiocyanate ions for perovskite/organic tandems with 25.06% efficiency - Zhang, Zhichao; Chen, Weijie; Jiang, Xingxing; Cao, Jianlei; Yang, Haidi; Chen, Haiyang; Yang, Fu; Shen, Yunxiu; Yang, Heyi; Cheng, Qinrong; Chen, Xining; Tang, Xiaohua; et al. (Nature Energy, 2024)
Mixed halide wide-bandgap perovskites are suitable for integration in tandem photovoltaics such as perovskite/organic tandem solar cells. However, halide phase segregation originating from halogen vacancy-assisted ion migration in wide-bandgap perovskites limits the device efficiency and lifetime. Here we incorporate pseudo-halogen thiocyanate (SCN) ions in iodide/bromide mixed halide perovskites and show that they enhance crystallization and reduce grain boundaries. Trace amount of SCN ions in the bulk enter the perovskite lattice, forming an I/Br/SCN alloy, and occupy iodine vacancies, blocking halide ion migration via steric hindrance. Taken together, these effects retard halide phase segregation under operation and reduce energy loss in the wide-bandgap perovskite cells. The resulting perovskite/organic tandem solar cell achieves a power conversion efficiency of 25.82% (certified 25.06%) and an operational stability of 1,000 h.
CRIS-Team Scopus Importer:2024-04-05

Suppression of Thermally Induced Fullerene Aggregation in Polyfullerene-Based Multiacceptor Organic Solar Cells - Dowland, Simon A.; Salvador, Michael Filipe; Perea Ospina, Jose Dario; Gasparini, Nicola; Langner, Stefan; Rajoelson, Sambatra; Ramanitra, Hasina H.; Lindner, Benjamin; Osvet, Andres; Brabec, Christoph; Hiorns, Roger C.; Egelhaaf, Hans-Joachim (ACS Applied Materials and Interfaces, 2017)
A novel main-chain polyfullerene, poly[fullerene-alt-2,5-bis(octyloxy)terephthalaldehyde] (PPC4), is investigated for its hypothesized superior morphological stability as an electron-accepting material in organic photovoltaics relative to the widely used fullerene phenyl-C61-butyric acid methyl ester (PCBM). When mixed with poly(3-hexylthiophene-2,5-diyl) (P3HT), PPC4 affords low-charge-generation yields because of poor intermixing within the blend. The adoption of a multiacceptor system, by introducing PCBM into the P3HT:polyfullerene blend, was found to lead to a 3-fold enhancement in charge generation, affording power conversion efficiencies very close to that of the prototypical P3HT:PCBM binary control. Upon thermal stressing and in contrast to the P3HT:PCBM binary, photovoltaic devices based on the multiacceptor system demonstrated significantly improved stability, outperforming the control because of suppression of the PCBM migration and aggregation processes responsible for rapid device failure. We rationalize the influence of the fullerene miscibility and its implications on the device performance in terms of a thermodynamic model based on Flory-Huggins solution theory. Finally, the potential universal applicability of this approach for thermal stabilization of organic solar cells is demonstrated, utilizing an alternative low-band-gap polymer-donor system.
Keywords: fullerene aggregation; main-chain polyfullerenes; multi acceptor composite blend; organic photovoltaics; thermal stability

Surface thermography using dual channel imaging based on the blue and red emission of Ba3MgSi2O8:Eu2+, Mn2+ - Hashemi, Amir; Gast, Jessica; Ali, Amjad; Osvet, Andres; Batentschuk, Miroslaw; Brabec, Christoph (Measurement Science and Technology, 2017)
In this investigation, we present a surface temperature determination method, based on the luminescence characteristics of Ba3MgSi2O8:Eu+2,Mn+2. Simple optics utilizing only one RGB scientific CMOS camera makes this measurement technique easily applicable. Four different imaging methods were developed and are presented together with the corresponding calibration curves. We successfully utilized the methods to take surface temperature gradient images of glass plates with a point heat source between them.
Keywords: Phosphor spectroscopy; Dual channel lock in method; Phase sensitive averaging detection method; Imaging; Temperature measurement; Photoluminescence decay; Intensity ratio

Surface versus Bulk Currents and Ionic Space-Charge Effects in CsPbBr3 Single Crystals - Almora Rodriguez, Osbel; Matt, Gebhard; These, Albert; Kanak, Andrii; Levchuk, Ievgen; Shrestha, Shreetu; Osvet, Andres; Brabec, Christoph; Garcia-Belmonte, Germa (Journal of Physical Chemistry Letters, 2022)
CsPbBr3 single crystals have potential for application in ionizing-radiation detection devices due to their optimal optoelectronic properties. Yet, their mixed ionic-electronic conductivity produces instability and hysteretic artifacts hindering the long-term device operation. Herein, we report an electrical characterization of CsPbBr3 single crystals operating up to the time scale of hours. Our fast time-of-flight measurements reveal bulk mobilities of 13-26 cm(2) V-1 s(-1) with a negative voltage bias dependency. By means of a guard ring (GR) configuration, we separate bulk and surface mobilities showing significant qualitative and quantitative transport differences. Our experiments of current transients and impedance spectroscopy indicate the formation of several regimes of space-charge-limited current (SCLC) associated with mechanisms similar to the Poole-Frenkel ionized-trap-assisted transport. We show that the ionic-SCLC seems to be an operational mode in this lead halide perovskite, despite the fact that experiments can be designed where the contribution of mobile ions to transport is negligible.
CRIS-Team WoS Importer:2022-06-10

Surpassing the 10% efficiency milestone for 1-cm2 all-polymer solar cells - Fan, Baobing; Zhong, Wenkai; Ying, Lei; Zhang, Difei; Li, Meijing; Lin, Yanrui; Xia, Ruoxi; Liu, Feng; Yip, Hin Lap; Li, Ning; Ma, Yuguang; Brabec, Christoph; et al. (Nature Communications, 2019)
Naphthalenediimide-based n-type polymeric semiconductors are extensively used for constructing high-performance all-polymer solar cells (all-PSCs). For such all-polymer systems, charge recombination can be reduced by using thinner active layers, yet suffering insufficient near-infrared light harvesting from the polymeric acceptor. Conversely, increasing the layer thickness overcomes the light harvesting issue, but at the cost of severe charge recombination effects. Here we demonstrate that to manage light propagation within all-PSCs, a thick bulk-heterojunction film of approximately 350 nm is needed to effectively enhance photo-harvesting in the near-infrared region. To overcome the severe charge recombination in such a thick film, a non-halogenic additive is used to induce a well-ordered micro-structure that inherently suppresses recombination loss. The combined strategies of light management and delicate morphology optimization lead to a promising efficiency over 10% for thick-film all-PSCs with active area of 1 cm2, showing great promise for future large-scale production and application of all-PSCs.
CRIS-Team Scopus Importer:2019-09-17

Surprising Efficiency Enhancement of Cu2ZnSn(S,Se)4 Solar Cells with Abnormal Zn/Sn Ratios - Ge, Sijie; Xu, Han; Huang, Yuxiang; Karunakaran, Santhosh Kumar; Hong, Ruijiang; Li, Jianjun; Mai, Yaohua; Gu, Ening; Lin, Xianzhong; Yang, Guowei (Solar RRL, 2020)
The elemental proportion of Cu poor and Zn rich in Cu2ZnSn(S,Se)4 (CZTSSe) is well established for achieving highly efficient CZTSSe solar cells. However, how high Zn/Sn ratio can the complicated CZTSSe thin film tolerate remains a question. Therefore, herein, the well control of Zn/Sn ratio in CZTSSe thin film is obtained by multi-spin-coating and tuning the initial Zn/Sn ratio in the Cu–Zn–Sn–S precursor ink from 1.0 to 1.9. It is found that the Zn/Sn on the surface of CZTSSe absorber can self-regulate to around 1.2 even with Zn/Sn ratio up to 1.9 in the precursor solution. Excess Zn presented as Zn(S,Se) secondary phase not only concentrate near the bottom area, but also widely distribute at the grain boundaries (GBs). In addition, it is found that the Zn(S,Se) secondary phase at GBs can promote current transport as revealed by conductive atomic force microscopy measurement. The surface roughness and grain size of the resulting CZTSSe absorber increased, whereas the MoSe2 thickness was reduced with increasing Zn/Sn ratio. More importantly, the device performance increased from 4.5% to 10.0% with a significant decrease in VOC deficit from 0.73 to 0.58 V when the Zn/Sn ratio increases from 1.0 to 1.5 in the precursor ink.
CRIS-Team Scopus Importer:2020-09-25
Keywords: CZTSSe solar cells; low V; self-regulation of surface compositions; Zn/Sn ratios

Suture retension test method for opthalmological materials - Voigt, Monika; Thieme, Daniel; Küng, Florian; Schubert, Dirk W.; Kruse, Friedrich; Fuchsluger, Thomas (Deutsche Gesellschaft für Biomaterialien, 2018)
Keywords: biomaterialien; espinning suture retension

Switching Off Hysteresis in Perovskite Solar Cells by Fine-Tuning Energy Levels of Extraction Layers - Guerrero, Antonio; Bou, Agustín; Matt, Gebhard; Almora, Osbel; Heumüller, Thomas; Garcia-Belmonte, Germà; Bisquert, Juan; Hou, Yi; Brabec, Christoph (Advanced Energy Materials, 2018)
Lead halide perovskites often suffer from a strong hysteretic behavior on their j–V response in photovoltaic devices that has been correlated with slow ion migration. The electron extraction layer has frequently been pointed to as the main culprit for the observed hysteretic behavior. In this work three hole transport layers are studied with well‐defined highest occupied molecular orbital (HOMO) levels and interestingly the hysteretic behavior is markedly different. Here it is shown that an adequate energy level alignment between the HOMO level of the extraction layer and the valence band of the perovskite, not only suppresses the hysteresis, avoiding charge accumulation at the interfaces, but also degradation of the hole transport layer is reduced. Numerical simulation suggests that formation of an injection barrier at the organic/perovskite heterointerface could be one mechanism causing hysteresis. The suppression of such barriers may require novel design rules for interface materials. Overall, this work highlights that both external contacts need to be carefully optimized in order to obtain hysteresis‐free perovskite devices.
Keywords: Charge accumulation; Hysteresis; Perovskites; Energy barrier; Hole extraction layer

Synthesis and Characterization of BaZrS3 Thin Films via Stacked Layer Methodology: A Comparative Study of BaZrS3 on Zirconium Foil and Silicon Carbide Substrates - Jamshaid, Sumbal; Cicconi, Maria Rita; Heiß, Wolfgang; Webber, Kyle Grant; Wellmann, Peter (Advanced Engineering Materials, 2024)
Chalcogenide perovskites are an emerging class of semiconductors particularly interesting for optoelectronic applications due to their high absorption coefficients and direct bandgaps of 1.7–1.9 eV. However, few processing routes have been developed for the synthesis of BaZrS3 thin films. The advances in the fabrication of BaZrS3 thin films using zirconium foil as precursor and substrate is a new strategy, which is compared with the results of BaZrS3 thin films deposited on silicon carbide (SiC) substrate. In this study, a stacked layer methodology, inspired by the fabrication methods used for chalcopyrites and kesterites, is employed. The main objective is to facilitate the conversion of these layers into the desired perovskite structure through annealing. In methodology, we initiated the process by depositing elemental Zr by sputtering on SiC, followed by BaS on top of the Zr through electron beam evaporation and then sulphurized and annealed at high temperature (≈1000–1050 °C) to form BaZrS3 in an inductively heated physical vapour transport setup in the presence of elemental sulphur. In the parallel approach the methodology remains same, with the sole deviation of zirconium foil, which act as both the substrate and the source. The successful synthesis of BaZrS3 is confirmed by X-Ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-Ray spectroscopy (EDS), while the optical band gap is analyzed by UV-Vis. The microstructure of the BaZrS3 films shows the polycrystalline structure and surface roughness.
CRIS-Team Scopus Importer:2024-04-12
Keywords: Barium Zirconium Trisulfide; BaZrS; chalcogenide perovskites; Ruddlesden–Popper phases

Synthesis and characterization of cellular apatite-whitlockite composites for bone substitution - Götz-Neunhoeffer, Friedlinde; Enderle, Ralph; Göbbels, Matthias (Schriftenreihe der Deutschen Gesellschaft für Geowissenschaften, 2005)
UnivIS-Import:2015-03-09:Pub.2005.nat.dgeo.IGM.LM.synthe_2

Synthesis and luminescent properties of prospective Ce3+ doped silicate garnet phosphors for white LED converters - Khaidukov, Nicholas; Zorenko, T.; Iskaliyeva, A.; Paprocki, K.; Batentschuk, Miroslaw; Osvet, Andres; Van Deun, R.; Zhydaczevskii, Ya.; Suchocki, Andrzej; Zorenko, Yu. (Journal of Luminescence, 2017)
The results on crystallization and investigation of the luminescent properties of prospective ceramic phosphors based on the Ce3+ doped Ca2R[ScB](CSi2)O12 (R = Lu, Y, Gd; B = Sc, Ga, C = Ga, Al) silicate garnets are presented for the first time in this work. We have observed the variations of the spectroscopic properties of Ce3+ ions in the mentioned Ca2+-Si4+ garnet hosts depending on the cation content at the dodecahedral , octahedral [] and tetrahedral () sites of garnet lattice. These results can be useful for the development of new generation of ceramic phosphor converters for white LEDs based on the garnet compounds under study.<br
Keywords: Ca-Si based garnet; Luminescence; Ce3+ dopant; LED ceramic converters

Synthesis and optical properties of luminescent core-shell structured silicate and phosphate nanoparticles - Dembski, Sofia; Rupp, Sabine; Milde, Moritz; Gellermann, Carsten; Dyrba, Marcel; Schweizer, Stefan; Batentschuk, Miroslaw; Osvet, Andres; Winnacker, Albrecht (Optical Materials, 2011)
Monodisperse, luminescent core–shell structured inorganic nanoparticles were synthesized by sol–gel technology. They exhibit an amorphous SiO2 core and a crystalline luminescent shell. Zn2SiO4:Mn2+ and Ca10(PO4)6OH:Eu3+ shell materials are investigated. The influence of the doping concentration on optical and structural properties was studied. The resulting nanoparticles were characterized by X-ray diffraction analysis, transmission electron microscopy, inductively coupled plasma optical emission spectrometry, and photoluminescence spectroscopy.<br
Keywords: Luminescent core-shell nanoparticles; Nanophosphor; Hydroxyapatite; Zn2SiO 4

Synthesis and photoluminescent properties of the Dy3+ doped YSO as a high-temperature thermographic phosphor - Chepyga, Liudmyla; Hertle, Ellen Elisabeth; Ali, Amjad; Zigan, Lars; Osvet, Andres; Brabec, Christoph; Batentschuk, Miroslaw (Journal of Luminescence, 2018)
Dy3+-doped yttrium orthosilicate (Y2SiO5, abbreviated YSO) phosphors were synthesized: (1) by conventional high temperature solid-state method using two types of fluxes: lithium fluoride (LiF) and boron oxide (B2O3); (2) by metal alkoxide sol-gel method using isopropoxide assisted co-precipitation with subsequent annealing to explore its possible application in high-temperature thermometry. It was experimentally observed that the use of LiF flux affects the luminescent properties due to improvement of the crystal quality of crystallites and co-doping Li+ and F- ions. Herein, a strategy involving the use of different fluxes and concentration of Dy3+ ions has been developed to achieve high photoluminescence (PL) intensity and high intensity ratio of different PL peaks. The case of incorporated LiF in the host crystal lattices revealed strong enhancement of luminescence intensity of YSO:Dy (more than three times higher at 293 K) compared to the luminescence intensity of the phosphors synthesized with B2O3. Based on the results of high temperature measurements, it can be stated that YSO:Dy is a favorable phosphor for high temperature measurement, with a temperature sensitivity range comparable to YAG:Dy but with a lower PL decay time which is reduced by about 60%. For temperatures up to 1250 K the intensity ratio approach offers better measurement capabilities while the temperature sensitivity above 1250 K is superior for the decay time approach.
Keywords: Dysprosium; Luminescence; Phosphor thermometry; YSO

Synthesis and photovoltaic effect in red/near-infrared absorbing A-D-A-D-A-type oligothiophenes containing benzothiadiazole and thienothiadiazole central units - Luponosov, Yuriy N.; Min, Jie; Khanin, Dmitry A.; Baran, Derya; Pisarev, Sergey A.; Peregudova, Svetlana M.; Dmitryakov, Petr V.; Chvalun, Sergei N.; Cherkaev, Georgiy V.; Svidchenko, Evgeniya A.; Ameri, Tayebeh; Brabec, Christoph; et al. (Journal of Photonics for Energy, 2015)
Two π-conjugated acceptor-donor-acceptor-donor-acceptor-type (A-D-A-D-A) oligothiophenes, TT-(2T-DCV-Hex) and BT-(2T-DCV-Hex) were designed and synthesized with thienothiadiazole (TT) or benzothiadiazole (BT) as the core and dicyanovinyl (DCV) as the terminal acceptor groups for comprehensively investigating and understanding structure-property relationships. The resulting oligomers were first characterized by thermal analysis, UV-Vis spectroscopy, and cyclic voltammetry. By simply changing the BT to TT core in these two oligothiophenes, the highest occupied molecular orbital levels were varied from-5.55 eV for BT-(2T-DCV-Hex) to-5.11 eV for TT-(2T-DCV-Hex), and the optical band gaps were varied from 1.72 eV for BT-(2T-DCV-Hex) to 1.25 eV for TT-(2T-DCV-Hex), ascribed to the stronger electron accepting character of the TT core. However, the power conversion efficiency of bulk heterojunction organic solar cells (OSCs) with TT-(2T-DCV-Hex) as donor and [6,6]-phenyl C70-butyric acid methyl ester (PC71BM) as acceptor was measured to be 0.04% only, which is much lower than that of BT-(2T-DCV-Hex):PC71BM (1.54%). Compared to the TT-(2T-DCV-Hex) system, the BT-(2T-DCV-Hex) based device shows smoother film surface morphology, and superior charge generation and charge carrier mobilities. Therefore, the results clearly demonstrate that in addition to modifying the alkyl side chains and p-bridge lengths, the design of new small molecules for high-performance OSCs should also aim to choose suitable acceptor units.
Keywords: benzothiadiazole; charge carrier mobility; charge generation; dicyanovinyl group; Donor-acceptor oligomer; organic solar cell; thienothiadiazole

Synthesis, characterization and optoelectronic properties of a new perylene diimide-benzimidazole type solar light harvesting dye - Dincalp, Haluk; Cimen, Oguzhan; Ameri, Tayebeh; Brabec, Christoph; Icli, Siddik (Spectrochimica Acta Part A-Molecular and Biomolecular Spectroscopy, 2014)
A perylene diimide type small molecule (BI-PDI) has been synthesized through Suzuki coupling reaction between N,N′-bis(2,6-diisopropylphenyl)- 1,7-dibromoperylene-3,4,9,10-tetracarboxylic diimide and 2-(2-hydroxyphenyl)-7- phenyl-1H-benzimidazole-4-boronic acid. BI-PDI small molecule has showed an absorption band between 350 and 750 nm on thin films. HOMO and LUMO energy levels of BI-PDI dye have been calculated to be about -5.92 eV and -3.82 eV, respectively. Solution-processed bulk heterojunction (BHJ) solar cells have been constructed using BI-PDI as donor and [6,6]-phenyl-C-butyric acid methyl ester (PCBM) as acceptor or poly(3-hexylthiophene) (P3HT) as donor and BI-PDI as acceptor. The external quantum efficiencies (EQE) of the devices cover the most of the visible region between 400 and 700 nm for both configurations. Photovoltaic performances of BI-PDI-based organic solar cells are limited by the aggregation tendency of PDI structure and poor hole/electron mobilities of the active layer. © 2014 Elsevier B.V. All rights reserved.
Keywords: Benzimidazole; Charge transfer; Light harvesting; Perylene diimide; Photoluminescence; Photovoltaics

Synthesis of BaZrS3 and BaS3 Thin Films: High and Low Temperature Approaches - Freund, Tim; Jamshaid, Sumbal; Monavvar, Milad; Wellmann, Peter (Crystals, 2024)
Current research efforts in the field of the semiconducting chalcogenide perovskites are directed towards the fabrication of thin films and subsequently determine their performance in the photovoltaic application. These efforts are motivated by the outstanding properties of this class of materials in terms of stability, high absorption coefficient near the band edge and no significant health concerns compared to their halide counterparts. The approach followed here is to use stacked precursor layers and is adopted from other chalcogenide photovoltaic materials like the kesterites and chalcopyrites. The successful synthesis of BaZrS3 from stacked layers of BaS and Zr and annealing at high temperatures ( 1100 °C) with the addition of elemental sulfur is demonstrated. However, the film shows the presence of secondary phases and a flawed surface. As an alternative to this, BaS3 could be used as precursor due to its low melting point of 554 °C. Previously, the fabrication of BaS3 films was demonstrated, but in order to utilize them in the fabrication of BaZrS3 thin films, their microstructure and processing are further improved in this work by reducing the synthesis temperature to 300 °C, resulting in a smoother surface. This work lays the groundwork for future research in the fabrication of chalcogenide perovskites utilizing stacked layers and BaS3.
CRIS-Team Scopus Importer:2024-04-05
Keywords: barium trisulphide; chalcogenide perovskites; stacked layers; thin films

Synthesis of Eu-doped SrAl2O4 nanophosphors by CO2 laser vaporization - Zollfrank, Cordt; Gruber, Sabine; Batentschuk, Miroslaw; Osvet, Andres; Götz-Neunhoeffer, Friedlinde; Dittrich, Sebastian; Grabow, Janet; Kurland, Heinz-Dieter; Müller, Frank A. (Acta Materialia, 2013)
A new method of synthesizing spherical nanoparticles with photoluminescent spinel structures using a CO2 laser co-vaporization technique (CoLAVA) is presented. The method applies homogeneous mixtures of oxidic precursors such as Al2O3, SrO and Eu2O 3 and allows the fabrication of quantities exceeding 10 g h -1. During the CoLAVA process, the educt oxides are reacted by a gas phase condensation yielding amorphous spherical particles with diameters ranging from 10 to 100 nm. The as-prepared materials exhibit red emission at 625 nm (1.98 eV) due to the incorporated Eu3+. Temperature treatment up to 1200 C under a reducing atmosphere yielded crystalline particles of the same size, which were slightly sintered. These particles consisted of >90 wt.% SrAl2O4 with minor fractions of Sr3Al 2O6 and SrCO3. The amount of the SrAl 2O4 spinel increased with increasing temperature, whereas the accompanying phases were decreased. A strong green emission centered at 525 nm (2.36 eV) detected at RT was observed at an onset temperature of 900 C, which is due to the presence of Eu2+ in the crystal lattice of SrAl 2O4. The red emission was not observed at higher annealing temperatures. The CoLAVA method represents a fast and facile route for the fabrication of nano- to microstructured phosphor materials for a variety of engineering applications. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2013.nat.dgeo.IGM.LM.synthe
Keywords: Laser vaporization; Nanoparticles; Photoluminescence

Synthesis of In2Se3 and Cu2-xSe Micro- and Nanoparticles with Microwave-Assisted Solvothermal and Aqueous Redox Reactions for the Preparation and Stabilization of Printable Precursors for a CuInSe2 Solar Cell Absorber Layer - Schuster, Matthias; Distaso, Monica; Möckel, Stefan; Künecke, Ulrike; Peukert, Wolfgang; Wellmann, Peter (2015)
Micro- and nanoparticles were synthesized and stabilized in order to process a copper indium diselenide (CISe) solar cell absorber layer. A microwave assisted solvothermal reaction for In2Se3 particles was performed, finding that smaller particles could be obtained in shorter times and at lower temperatures than with a conventional autoclave based solvothermal synthesis. In a second route In2Se3 and Cu2-xSe nanoparticles have been synthesized via aqueous redox reactions and been Zeta potential-stabilized to acquire a nanoparticulate ink. This ink was drop cast in ambient atmosphere and annealed in N-2-atmosphere leading to the formation of CISe at lower temperatures than with state-of-the-art processing routes. (C) 2015 Published by Elsevier Ltd.
Keywords: In2Se3; Cu2-xSe; nanoparticles; microwave; Zeta potential; low temperature; CuInSe2; solar cell

Synthesis of In2Se3 and Cu2-xSe Micro- and Nanoparticles with Microwave-Assisted Solvothermal and Aqueous Redox Reactions for the Preparation and Stabilization of Printable Precursors for a CuInSe2 Solar Cell Absorber Layer - Schuster, Matthias; Distaso, Monica; Möckel, Stefan; Künecke, Ulrike; Peukert, Wolfgang; Wellmann, Peter (Energy Procedia, 2015)
Micro- and nanoparticles were synthesized and stabilized in order to process a copper indium diselenide (CISe) solar cell absorber layer. A microwave assisted solvothermal reaction for In2Se3 particles was performed, finding that smaller particles could be obtained in shorter times and at lower temperatures than with a conventional autoclave based solvothermal synthesis. In a second route In2Se3 and Cu2-xSe nanoparticles have been synthesized via aqueous redox reactions and been Zeta potential-stabilized to acquire a nanoparticulate ink. This ink was drop cast in ambient atmosphere and annealed in N2 -atmosphere leading to the formation of CISe at lower temperatures than with state-of-the-art processing route
Keywords: In2Se3; Cu2-xSe; nanoparticles; microwave; Zeta potential; low temperature; CuInSe2; solar cell

Systematic Analysis of Polymer Molecular Weight Influence on the Organic Photovoltaic Performance - Katsouras, Athanasios; Gasparini, Nicola; Koulogiannis, Chrysanthos; Spanos, Michael; Ameri, Tayebeh; Brabec, Christoph; Chochos, Christos L.; Avgeropoulos, Apostolos (Macromolecular Rapid Communications, 2015)
The molecular weight of an electron donor-conjugated polymer is as essential as other well-known parameters in the chemical structure of the polymer, such as length and the nature of any side groups (alkyl chains) positioned on the polymeric backbone, as well as their placement, relative strength, the ratio of the donor and acceptor moieties in the backbone of donor-acceptor (D-A)-conjugated polymers, and the arrangement of their energy levels for organic photovoltaic performance. Finding the "optimal" molecular weight for a specific conjugated polymer is an important aspect for the development of novel photovoltaic polymers. Therefore, it is evident that the chemistry of functional conjugated polymers faces major challenges and materials have to adopt a broad range of specifications in order to be established for high photovoltaic performance. In this review, the approaches followed for enhancing the molecular weight of electron-donor polymers are presented in detail, as well as how this influences the optoelectronic properties, charge transport properties, structural conformation, morphology, and the photovoltaic performance of the active layer. Approaches followed for enhancing the molecular weight of the electron donor polymers and how this influences their optoelectronic properties, charge transport properties, structural conformation, morphology, and the photovoltaic performance of the active layer are analyzed and presented in detail.
Keywords: donor-acceptor; molecular weight; organic photovoltaics; polymers

Tailoring doped organic nanoparticles as selective hole transporters for printed non-fullerene organic solar cells - Xu, Junyi; Späth, Andreas; Gruber, Wolfgang; Barabash, Anastasia; Stadler, Philipp; Gubanov, Kirill; Wu, Mingjian; Forberich, Karen; Spiecker, Erdmann; Fink, Rainer H.; Unruh, Tobias; McCulloch, Iain; et al. (Nano Energy, 2023)
Keywords: Inverted structure; Organic nanoparticle; Doping; Organic solar cell; Solution-processed hole transporting layer

Tailoring green formulation: Printing and upscaling of inverted organic solar cells - Voigt, Monika; Machui, Florian; Lucera, Luca; Spyropoulos, Georgios; Cordero, Johann; Kubis, Peter; Ali, Abid Shaukat; Shalan, Ahmed E.; Brabec, Christoph (39th IEEE Photovoltaic Specialists Conference, PVSC 2013, 2013)
By tailoring the solvents of active organic solar cell layers regarding their solubility (Hansen parameters), non-halogenated solvents and solvent mixtures can be used to print the active layers of organic solar cells. Similar efficiencies to other typical laboratory methods as spin-coating can be reached. Furthermore, using sheet-to-sheet printing or coating techniques compatible to mass-manufacturing and structuring by laser ablation, we can upscale to 10×20 cm and manufacture modules on plastic substrates. This is a breakthrough for organic solar cells and the next important step on the way to utilize organic solar cells for industrial manufacturing. © 2013 IEEE.
Keywords: Green solvents; P3HT:PCBM; Photovoltaic cells; Printing; Simulation; Solubility

Tailoring the Charge Transport Properties of Printable Si-NCs By Conjugated Organic Ligands - Makhdoom, Atif; Sgobba, Vito; Khanzada, Laraib Sarfraz; Fladischer, Stefanie; Spiecker, Erdmann (physica status solidi (a), 2019)
Silicon is dominating the world in photovoltaic technology. The widely used mono crystalline and poly crystalline wafer technologies are expensive to process. As an alternative, technology of silicon nanocrystals (Si-NCs) is a necessity for economical processing of PV modules. In this work, commercially prepared Si-NCs with a mean diameter of 60 nm is utilized with a pretreatment process followed by functionalization. Styryl and 1-ethenyl-4-fluoro benzyl conjugate moieties are grafted on hydrogen-terminated Si-NCs via hydrosilylation of phenylacetylene and 1-ethyny1-4-fluoro benzene, respectively. Thick-films of these functionalized Si-NCs with different thicknesses are prepared and analyzed in a purposed device architecture at room temperature which reveals a p-type character of functionalized Si-NCs films. Detail analysis of current density voltage U V) characteristics of styryl functionalized Si-NCs films shows that the drifting of charge carriers follows a power law relationship V") in the presence of exponentially distributed trap states. Moreover, a unique voltage dependence of the J V curves also reveals a transition between direct and Fowler Nordheim (F N) tunneling mechanisms.
Keywords: 1-ethynyl-4-fluoro benzene; hydrosilylation; phenylacetylene; silicon nanocrystals; space-charge-limited conduction

Tailoring the Dimensionality of 2D/3D Heterojunctions for Inverted Perovskite Solar Cells - Li, Chaohui; Zhang, Kaicheng; Maiti, Santanu; Peng, Zijian; Tian, Jingjing; Park, Hyoungwon; Byun, Jiwon; Xie, Zhiqiang; Dong, Lirong; Qiu, Shudi; Bornschlegl, Andreas; Liu, Chao; et al. (ACS Energy Letters, 2024)
Interface engineering is crucial to achieving stable perovskite photovoltaic devices. A versatile approach is developed to tailor interface properties via integrating co-assembled monolayers (co-SAMs) at the p-type buried interface and by capping a two-dimensional (2D) perovskite layer at the n-type upper interface with vacuum quenching. Optimized co-SAMs promote the coverage of the hole transport layer, significantly reducing the incidence of leakage currents. Based on this foundation, we develop damp-heat-stable perovskite solar cells by precisely tailoring the fragments of 2D perovskite layers through vacuum annealing with phenethylammonium iodide. An impressive open-circuit voltage of 1.216 V is achieved, corresponding to 92% of the value determined by the detailed-balance limit, along with a power conversion efficiency of 23.68%. Ultimately, integrating co-SAMs and the vacuum-assisted annealing fabricated devices maintain 96% and 80% of initial efficiencies after 1200 and 500 h of tracking at a maximum power point under 55 and 85 °C, respectively.
CRIS-Team Scopus Importer:2024-02-23

Tailoring the Nature of Interface States in Efficient and Stable Bilayer Organic Solar Cells by a Transfer-Printing Technique - Wang, Rong; Jiang, Youyu; Gruber, Wolfgang; He, Yakun; Wu, Mingjian; Weitz, Paul; Zhang, Kaicheng; Lüer, Larry; Forberich, Karen; Unruh, Tobias; Spiecker, Erdmann; Deibel, Carsten; et al. (Advanced Materials Interfaces, 2022)
Bulk heterojunction organic solar cells (BHJ-OSCs) are designed to overcome inefficient charge generation and limited exciton diffusion of organic semiconductors. However, there are some disadvantages involving inherent voltage losses, microstructure control, and operational instability. Bilayer solar cells (BL-OSCs) without mixed regions are free from these problems and offer a platform to explore the photophysical processes at the donor-acceptor interface. Here, a breakthrough for n-i-p BL-OSCs in charge generation efficiency is reported. A gradual adjustment of the molecular interface orientation of the polymer donor (PM6) is accompanied by the evolution of charge-transfer states and Forster energy transfer. Besides, less recombination losses and superior morphological stability of BL-OSCs are achieved at a PCE comparable to that of BHJ-OSCs with similar layer thickness. This investigation confirms the feasibility of manufacturing BL-OSCs by a transfer printing method and provides a versatile architecture to study fundamental interface phenomena in OSCs independent from microstructure disorder.
CRIS-Team WoS Importer:2022-04-29

Targeted Adjusting Molecular Arrangement in Organic Solar Cells via a Universal Solid Additive - Zhang, Difei; Li, Yuanfeng; Li, Meijing; Zhong, Wenkai; Heumüller, Thomas; Li, Ning; Ying, Lei; Brabec, Christoph; Huang, Fei (Advanced Functional Materials, 2022)
The incorporation of solid additive has been considered as an effective strategy for developing organic photovoltaics with multi-components, which is independent of dynamics, playing unique roles in morphology adjustment. However, their complex working mechanisms involving specific chemical structures are selective to material systems, hence limiting their university and flexibility in application. Herein, an inert small-molecular compound naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole (NT) is introduced into the bulk-heterojunction blend as the solid additive, which can function with various material systems and solvents, depending on its simple π-conjugated structure and S⋯N interaction for adjusting molecular alignment. It is interesting to note that the introduced NT can not only improve device performance, but also simplify complicated pre- or post-processing methods, reduce impact from batch-to-batch differences, construct sufficient energy transfer channel as well as improve device stability. The resulting devices based on PTzBI-dF:Y6-BO system show an impressive power conversion efficiency of 17.4% with obviously enhanced T80 lifetime of >1200 h. These findings provide useful guidelines for exploring potential universal solid additives benefitting toward commercial application.
CRIS-Team Scopus Importer:2022-07-22
Keywords: device stability; morphology evolution; non-fullerene acceptors; organic solar cells; solid additives

Technology-dependent analysis of the snow melting and sliding behavior on photovoltaic modules - Bogenrieder, Josef; Camus, Christian; Huettner, Maximilian; Offermann, Pascal; Brabec, Christoph; Hauch, Jens (Journal of Renewable and Sustainable Energy, 2018)
In this study, the snow melting behavior of several photovoltaic technologies, all installed at the same location under identical conditions, is analyzed based on the time-dependent changes of the snow cover, which is extracted from images of a monitoring webcam, for various temperature and irradiation conditions. From this study, conclusions can be drawn for the optimum module technology for a given location with respect to snow-dependent yield losses. In particular, the melting behavior is analyzed regarding its dependence on the ambient temperature and the irradiation level. Finally, the relevance of snow cover-related losses is discussed. The study shows that comparably large frameless modules exhibit the highest snow shedding rates. Hence, they are snow-free for longer periods, thereby increasing their potential for electricity generation in snowy regions. In summary, this paper reveals the beneficial snow removal properties of large frameless modules for snowy areas by applying a novel image processing technique for the determination of the snow-covered area fraction of the modules. Published by AIP Publishing.

Technology-specific yield analysis of various photovoltaic module technologies under specific real weather conditions - Bogenrieder, Josef; Hüttner, M.; Luchscheider, Philipp; Hauch, Jens; Camus, Christian; Brabec, Christoph (Progress in Photovoltaics: Research and Applications, 2017)
In the presented paper, we introduce an approach to rate the performance of modules under specific real weather conditions, since solar modules are rated according to standard test conditions which do not give evidence of the performance under real outdoor conditions. Therefore,we categorize the daily weather at a photovoltaic test site into 7 different climatic-day classifications and multiple cloud scenarios. Two different approaches to evaluate the cloud conditions were investigated. Furthermore, we use the developed approach to rate the performance of 8 different commercially available photovoltaic modules that have been installed and measured in Germany. The evaluation shows that module properties (eg, temperature coefficient, spectral response, and mechanical construction) have a major influence on the performance of photovoltaic modules under different weather conditions.
Keywords: climate; outdoor; performance; photovoltaics; weather; yield analysis

Temperature-dependent luminescence characteristics of Dy3+ doped in various crystalline hosts - Hertle, Ellen Elisabeth; Chepyga, Liudmyla; Batentschuk, Miroslaw; Will, Stefan; Zigan, Lars (Journal of Luminescence, 2018)
The effects of the crystalline host and the incorporation of a sensitizer (Er3+,Pr3+) on the temperature-dependent luminescence characteristics of Dy3+ were studied in a temperature range of 300–1650 K. Special emphasis was put on the usability of the respective materials as an optical temperature sensor, especially for extreme environments at high temperatures. Five base hosts, namely YAG, YAP, YSO, YSZ and CASO were evaluated and slightly varied regarding the host compounds (e.g. by adding B3+-N3−) or by adding a sensitizer. Particle sizes and morphology were studied using scanning electron microscope imaging and X-ray diffractometry. Excitation spectra and temperature-dependent luminescence emission were recorded and analyzed with respect to absolute intensities, lifetime, intensity ratio and sensitivity. The best combination regarding low lifetime and high quenching temperature, absolute intensity and sensitivity was observed for YAP:Dy3+ and variations of YAG:Dy3+ with either incorporation of B3+-N3− in the host compound or the addition of Er3+ as a sensitiz
Keywords: Optical sensor; Phosphor thermometry; Dy3+; Host matrix

Temperature-dependent optical spectra of single-crystal (CH3NH3)PbBr3 cleaved in ultrahigh vacuum - Niesner, Daniel; Schuster, Oskar; Wilhelm, Max; Levchuk, Ievgen; Osvet, Andres; Shrestha, Shreetu; Batentschuk, Miroslaw; Brabec, Christoph; Fauster, Thomas (Physical Review B - Condensed Matter and Materials Physics, 2017)
We measure temperature-dependent one-photon and two-photon induced photoluminescence from (CH3NH3)PbBr3 single crystals cleaved in ultrahigh vacuum. An approach is presented to extract absorption spectra from a comparison of both measurements. Cleaved crystals exhibit broad photoluminescence spectra. We identify the direct optical band gap of 2.31 eV. Below 200 K, the band gap increases with temperature, and it decreases at elevated temperature, as described by the Bose-Einstein model. An excitonic transition is found 22 meV below the band gap at temperatures <200 K. Defect emission occurs at photon energies <2.16 eV. In addition, we observe a transition at 2.25 eV (2.22 eV) in the orthorhombic (tetragonal and cubic) phase. Below 200 K, the associated exciton binding energy is also 22 meV, and the transition redshifts at higher temperature. The binding energy of the exciton related to the direct band gap, in contrast, decreases in the cubic phase. High-energy emission from free carriers is observed with higher intensity than reported in earlier studies. It disappears after exposing the crystals to ai

Temperature measurements using YAG : Dy and YAG : Sm under diode laser excitation (405 nm) - Hashemi, Amir; Vetter, Andreas; Jovicic, Gordana; Batentschuk, Miroslaw; Brabec, Christoph (Measurement Science & Technology, 2015)
Temperature-sensitive phosphors offer an option of accurate contactless temperature measurement. The method can be applied to a wide temperature range and up to more than 1500 K. In the current paper, phosphor thermometry based on four rare earths doped in YAG was studied. The standard excitation of thermographic phosphors is carried out with a Nd : YAG laser often at 355 or 266 nm. We examined the temperature dependent luminescence at an excitation wavelength of 405 nm. The excitation with visible blue light offers two main advantages: the excitation sources are rather cheap and they involve less safety issues. Accordingly, a variety of new application of such remote-thermometry would be possible. The results show that YAG : Dy and YAG : Sm may be well utilized for phosphor thermometry excited by a 405 nm diode laser.
Keywords: phosphor thermometry; temperature; luminescence; phosphorescence; diode laser

Ternary All-Polymer Solar Cells With 8.5% Power Conversion Efficiency and Excellent Thermal Stability - Liu, Xi; Zhang, Chaohong; Pang, Shuting; Li, Ning; Brabec, Christoph; Duan, Chunhui; Huang, Fei; Cao, Yong (Frontiers in Chemistry, 2020)
All-polymer solar cells (all-PSCs) composed of polymer donors and acceptors have attracted widespread attention in recent years. However, the broad and efficient photon utilization of polymer:polymer blend films remains challenging. In our previous work, we developed NOE10, a linear oligoethylene oxide (OE) side-chain modified naphthalene diimide (NDI)-based polymer acceptor which exhibited a power conversion efficiency (PCE) of 8.1% when blended with a wide-bandgap polymer donor PBDT-TAZ. Herein, we report a ternary all-PSC strategy of incorporating a state-of-the-art narrow bandgap polymer (PTB7-Th) into the PBDT-TAZ:NOE10 binary system, which enables 8.5% PCEs within a broad ternary polymer ratio. We further demonstrate that, compared to the binary system, the improved photovoltaic performance of ternary all-PSCs benefits from the combined effect of enhanced photon absorption, more efficient charge generation, and balanced charge transport. Meanwhile, similar to the binary system, the ternary all-PSC also shows excellent thermal stability, maintaining 98% initial PCE after aging for 300 h at 65°C. This work demonstrates that the introduction of a narrow-bandgap polymer as a third photoactive component into ternary all-PSCs is an effective strategy to realize highly efficient and stable all-PSCs.
CRIS-Team Scopus Importer:2020-05-15
Keywords: all-polymer solar cells; Förster resonant energy transfer; power conversion efficiency; ternary solar cells; thermal stability

The 2021 flexible and printed electronics roadmap - Bonnassieux, Yvan; Brabec, Christoph; Cao, Yong; Carmichael, Tricia Breen; Chabinyc, Michael L.; Cheng, Kwang Ting; Cho, Gyoujin; Chung, Anjung; Cobb, Corie L.; Distler, Andreas; Egelhaaf, Hans-Joachim; Grau, Gerd; et al. (Flexible and Printed Electronics, 2021)
This roadmap includes the perspectives and visions of leading researchers in the key areas of flexible and printable electronics. The covered topics are broadly organized by the device technologies (sections 1–9), fabrication techniques (sections 10–12), and design and modeling approaches (sections 13 and 14) essential to the future development of new applications leveraging flexible electronics (FE). The interdisciplinary nature of this field involves everything from fundamental scientific discoveries to engineering challenges; from design and synthesis of new materials via novel device design to modelling and digital manufacturing of integrated systems. As such, this roadmap aims to serve as a resource on the current status and future challenges in the areas covered by the roadmap and to highlight the breadth and wide-ranging opportunities made available by FE technologies.
CRIS-Team Scopus Importer:2021-06-25
Keywords: E-textiles; Flexible and printed electronics; Organic light emitting diodes; Organic photovoltaics; Roll-to-roll printing; Sensors; Thin film transistors

The 50th Anniversary of the German Association for Crystal Growth, DGKK - Danilewsky, Andreas; Wellmann, Peter; Miller, Wolfram (Crystal Research and Technology, 2020)
CRIS-Team WoS Importer:2020-04-03

The effect of organic and metal oxide interfacial layers on the performance of inverted organic photovoltaics - Savva, Achilleas; Petraki, Foteini; Elefteriou, Polyvios; Sygellou, Lambrini; Voigt, Monika; Giannouli, Myrsini; Kennou, Stella; Nelson, Jenny; Bradley, Donal D. C.; Brabec, Christoph; Choulis, Stelios A. (Advanced Energy Materials, 2013)
We study the origin of the improvement of the power conversion effi ciency (PCE) of inverted organic solar cells when an interfacial insulating organic layer of polyoxyethylene tridecyl ether (PTE) is introduced between the indium tin oxide (ITO) bottom electrode and the TiOx interfacial layer. XPS and UPS measurements are used to investigate the energy level alignment at the interfaces within the ITO/TiOx and ITO/PTE/TiOx structures and to identify any effects due to chemical interaction and interfacial dipoles. Scanning electron microscopy studies show that the surface structure of the TiOx layer is affected, when it is coated on top of the PTE layer. Surface contact angle measurements show that the incorporated interfacial layer of PTE is more hydrophilic than ITO and thus PTE modifi ed TiO x becomes more hydrophilic. This, in combination with the surface gaps of the PTE interfacial layer, is likely to lead to changed wetting and hydrolysis properties of TiOx when coated on ITO/PTE than on ITO alone. The different TiOx layer quality is refl ected in improved electron selectivity, leading to enhanced fi ll factor, reduced parasitic resistance effects and higher power conversion effi ciency for inverted solar cells with a PTE interfacial layer between ITO and TiOx. © 2013 WILEY-VCH Verlag GmbH and Co. © 2013 WILEY-VCH Verlag GmbH & Co.
CRIS-Team Scopus Importer:2023-03-07

The effect of oxygen induced degradation on charge carrier dynamics in P3HT:PCBM and Si-PCPDTBT:PCBM thin films and solar cells - Karuthedath, Safakath; Sauermann, Tobias; Egelhaaf, Hans-Joachim; Wannemacher, Reinhold; Brabec, Christoph; Lueer, Larry (Journal of Materials Chemistry A, 2015)
Due to their light weight, transparency and flexibility, organic photovoltaic (OPV) devices are ideal for building integration. As this application requires solar cell life times of more than twenty years and oxygen ingress cannot be avoided at competitive cost on this time scale, OPV modules must be intrinsically stabilized against photo-oxidation. To this end, the mechanism of rapid performance loss of OSCs due to oxygen-induced degradation must be understood. Here, we combine transient absorption experiments with electrical studies in P3HT:PCBM and Si-PCPDTBT:PCBM thin films and solar cells after controlled photo-oxidation, studying charge carrier dynamics on the femtosecond to millisecond time scale. We find that oxygen-induced degradation does not significantly influence charge generation, while its influence on charge recombination is strong in both materials. A dramatic retardation of charge recombination already at low levels of oxygen-induced degradation is attributed to a substantial reduction of charge mobilities. We also observe a significant increase of the background concentration of charge carriers with the level of degradation, which leads to a crossover from second order towards pseudo-first order recombination behaviour. Extraction is shown to be retarded even more strongly than recombination, possibly by a reduction of the extraction field by the background carriers. Overall, the recombination yield is increased with degradation, explaining the strong performance loss already at low degradation levels.
Keywords: Engineering controlled terms: Charge carriers; Extraction; Oxygen; Silicon; Thin films Background concentration; Building integration; Charge carrier dynamics; Charge recombinations; Induced degradation; Organic photovoltaic devices; Substantial reduction; Transient absorption Engineering main heading: Solar cells

The Effect of PCBM Dimerization on the Performance of Bulk Heterojunction Solar Cells - Distler, Andreas; Sauermann, Tobias; Egelhaaf, Hans-Joachim; Rodman, Sheila; Waller, Dave; Cheon, Kap-Soo; Lee, Mike; Guldi, Dirk Michael (Advanced Energy Materials, 2013)
Increasing the lifetime of polymer based organic solar cells is still a major challenge. Here, the photostability of bulk heterojunction solar cells based on the polymer poly[4,4'-bis(2-ethylhexyl)dithieno[3,2-b:2',3'-d]silole)-2,6-diyl-alt-[2,5-bis(3-tetradecylthiophen-2-yl)thiazole[5,4-d]thiazole)-1,8-diyl] (PDTSTzTz) and the fullerene [6,6]-phenyl-C-butyric acid methyl ester (PCBM) under inert atmosphere is investigated. Correlation of electrical measurements on complete devices and UV-vis absorption measurements as well as high-performance liquid chromatography (HPLC) analysis on the active materials reveals that photodimerization of PCBM is responsible for the observed degradation. Simulation of the electrical device parameters shows that this dimerization results in a significant reduction of the charge carrier mobility. Both the dimerization and the associated device performance loss turn out to be reversible upon annealing. BisPCBM, the bis-substituted analog of PCBM, is shown to be resistant towards light exposure, which in turn enables the manufacture of photostable PDTSTzTz:bisPCBM solar cells. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

The Effect of Silicon Substitution in Indacenodithiophene-Based A2-A1-D-A1-A2-Type Nonfullerene Acceptors on the Performance of High-Voltage Organic Solar Cells - Dai, Tingting; Du, Mengzhen; Wang, Helin; Li, Xianda; He, Zehua; Meng, Yuhan; Yang, Fu; Tang, Ailing; Geng, Yanfang; Zhou, Erjun (Solar RRL, 2022)
In recent years, the organic solar cells (OSCs) research hotspot is the modification of end groups and alkyl side chains of A-DA’D-A-type nonfullerene acceptors (NFAs). However, the development of novel NFAs by changing the different bridged atom substitution of the central core is lagging behind. Herein, two wide-bandgap A2-A1-D-A1-A2-type NFAs with different central cores, namely BTA501 and BTA502, are developed to improve the photovoltaic performance of high-voltage OSCs. BTA501 adopted an indacenodithiophene (IDT) core, whereas BTA502 applied a silaindacenodithiophene (SiIDT) core. Expectedly, the SiIDT-based BTA502 exhibits a higher lowest unoccupied molecular orbital level and wider bandgap than BTA501, which thus enhances the open-circuit voltage (V OC) but slightly decreases the short-circuit current density (J SC) of OSCs. Moreover, the stronger self-aggregation characteristics and weaker π–π stacking of BTA502 severely affect the exciton dissociation and charge transport. When blended with two classic p-type polymers J52-F and PTB7-Th, both combinations based on BTA502 exhibit inferior device performance compared with BTA501. Excitingly, the device of J52-F: BTA501 achieves a V OC of 1.037 V with a power conversion efficiency of 11.82% and a J SC of 15.89 mA cm−2, which are among the highest values for high-voltage OSCs with V OC above 1.0 V.
CRIS-Team Scopus Importer:2022-10-07
Keywords: high-voltage systems; indacenodithiophene; nonfullerene acceptors; organic photovolatic cells; silaindacenodithiophene

The evolution of Materials Acceleration Platforms: toward the laboratory of the future with AMANDA - Wagner, Jerrit; Berger, Christian; Du, Xiaoyan; Stubhan, Tobias; Hauch, Jens; Brabec, Christoph (Journal of Materials Science, 2021)
The development of complex functional materials poses a multi-objective optimization problem in a large multi-dimensional parameter space. Solving it requires reproducible, user-independent laboratory work and intelligent preselection of experiments. However, experimental materials science is a field where manual routines are still predominant, although other domains like pharmacy or chemistry have long used robotics and automation. As the number of publications on Materials Acceleration Platforms (MAPs) increases steadily, we review selected systems and fit them into the stages of a general material development process to examine the evolution of MAPs. Subsequently, we present our approach to laboratory automation in materials science. We introduce AMANDA (Autonomous Materials and Device Application Platform - www.amanda-platform.com), a generic platform for distributed materials research comprising a self-developed software backbone and several MAPs. One of them, LineOne (L1), is specifically designed to produce and characterize solution-processed thin-film devices like organic solar cells (OSC). It is designed to perform precise closed-loop screenings of up to 272 device variations per day yet allows further upscaling. Each individual solar cell is fully characterized, and all process steps are comprehensively documented. We want to demonstrate the capabilities of AMANDA L1 with OSCs based on PM6:Y6 with 13.7% efficiency when processed in air. Further, we discuss challenges and opportunities of highly automated research platforms and elaborate on the future integration of additional techniques, methods and algorithms in order to advance to fully autonomous self-optimizing systems—a paradigm shift in functional materials development leading to the laboratory of the future.
CRIS-Team Scopus Importer:2021-08-06

The Evolution of Tin-Based Perovskites Solar Cells - Li, Chaohui; Feng, Mingjie; Guo, Fei; Jiang, Qinglong; Li, Ning; Guo, Zhanhu; Liu, Xianhu (Engineered Science, 2022)
CRIS-Team Scopus Importer:2022-07-01

The fabrication of color-tunable organic light-emitting diode displays via solution processing - Guo, Fei; Karl, André; Xue, Qifan; Tam, Kai C.; Forberich, Karen; Brabec, Christoph (Light: Science & Applications, 2017)
Electroluminescent devices based on organic semiconductors have attracted significant attention owing to their promising applications in flat-panel displays. The conventional display pixel consisting of side-by-side arrayed red, green and blue subpixels represents the mature technology but bears an intrinsic deficiency of a low pixel density. Constructing an individual color-tunable pixel that comprises vertically stacked subpixels is considered an advanced technology. Although color-tunable organic light-emitting diodes (OLEDs) have been fabricated using the vacuum deposition of small molecules, the solution processing of conjugated polymers would enable a much simpler and inexpensive manufacturing process. Here we present the all-solution processing of color-tunable OLEDs comprising two vertically stacked polymer emitters. A thin layer of highly conducting and transparent silver nanowires is introduced as the intermediate charge injection contact, which allows the emission spectrum and intensity of the tandem devices to be seamlessly manipulated. To demonstrate a viable application of this technology, a 4-by-4 pixelated matrix color-tunable display was fabricated.
Keywords: color tunable; oLED display; organic light-emitting diode; silver nanowires; solution processing; tandem

The Fine-Structure Constant as a Ruler for the Band-Edge Light Absorption Strength of Bulk and Quantum-Confined Semiconductors - Prins, P. Tim; Alimoradi Jazi, Maryam; Killilea, Niall Andrew; Evers, Wiel H.; Geiregat, Pieter; Heiß, Wolfgang; Houtepen, Arjan J.; Delerue, Christophe; Hens, Zeger; Vanmaekelbergh, Daniel (Nano Letters, 2021)
Low-dimensional semiconductors have found numerous applications in optoelectronics. However, a quantitative comparison of the absorption strength of low-dimensional versus bulk semiconductors has remained elusive. Here, we report generality in the band-edge light absorptance of semiconductors, independent of their dimensions. First, we provide atomistic tight-binding calculations that show that the absorptance of semiconductor quantum wells equals mπα (m = 1 or 2 with α as the fine-structure constant), in agreement with reported experimental results. Then, we show experimentally that a monolayer (superlattice) of quantum dots has similar absorptance, suggesting an absorptance quantum of mπα per (confined) exciton diameter. Extending this idea to bulk semiconductors, we experimentally demonstrate that an absorptance quantum equal to mπα per exciton Bohr diameter explains their widely varying absorption coefficients. We thus provided compelling evidence that the absorptance quantum πα per exciton diameter rules the band-edge absorption of all direct semiconductors, regardless of their dimension.
CRIS-Team Scopus Importer:2021-12-17
Keywords: dielectric screening; fine-structure constant; light absorption; optical transitions; quantum coupling

The formation of CuInSe2 thin-film solar cell absorbers by laser annealing of electrodeposited precursors - Jost, Stefan Georg; Schurr, R.; Hergert, Frank; Hock, Rainer; Schulze, J.; Kirbs, A.; Voss, T.; Purwins, Michael; Palm, J.; Mys, I. (Solar Energy Materials and Solar Cells, 2008)
The formation of the compound semiconductor CuInSe2 by laser annealing of electroplated precursor films in inert gas atmosphere represents an entire non-vacuum production process of thin-film solar cell absorbers. Besides this technological aspect, the impact of extreme annealing rates on structural properties of the resulting semiconductor is interesting from a fundamental research point of view. For this reason, we compared absorbers processed by laser annealing with absorbers annealed with moderate heating rates in the range of 1 K/s by means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). All absorbers processed with laser or furnace annealing consist of crystalline CuInSe2 in the chalcopyrite crystal structure with a high degree of cation disorder. We show that laser annealing does not lead to unintentional selenium loss during the semiconductor formation process. (c) 2007 Elsevier B.V. All rights reserved.
Keywords: CuInSe2; thin films; laser annealing; electrodeposition; non-vacuum processing

The formation of the thin-film solar cell absorber CuInS2 by annealing of Cu-In-S stacked elemental layer precursors - A comparison of selenisation and sulfurisation - Jost, S.; Schurr, R.; Hölzing, Astrid; Hergert, Frank; Hock, Rainer; Purwins, Michael; Palm, J. (ELSEVIER SCIENCE SA, 2009)
We present results of in-situ X-ray diffraction experiments on the formation of CuInS2 thin film solar cell absorbers. The experiments have been performed while annealing Cu-In-S stacked elemental layer precursors produced by sputtering and thermal evaporation to investigate the crystallisation process of the chalcopyrite CuInS2. Rietveld refinement has been performed to obtain the quantitative phase evolution of crystalline phases while annealing. The annealing process is characterised by a rapid sulfurisation of the initially present intermetallic alloy Cu11In9 forming the sulfide phases CuS, Dg-Cu2-xS, InS and/or CuIn5S8. The chalcopyrite CuInS2 crystallises at elevated sample temperatures by the consumption of these sulfide phases as educts. Three different chalcopyrite formation reactions have been identified by an analysis of the quantitative phase evolution. A comparison to earlier investigations on the formation of CuInSe2 from Cu-In-Se precursors is presented to show similarities and differences of sulfurisation and selenisation processes. The chalcopyrite forms from chalcogenide educts in both cases. However, distinct differences concerning the chalcogenisation kinetics of sulfur and selenium containing Cu-In precursors have been revealed. The chalcogenisation of the intermetallic alloy phase Culling proceeds extremely fast for Cu-In-S precursors as compared to Cu-In-Se samples. (C) 2008 Elsevier B.V. All lights reserved.
Keywords: CuInS2; Chalcopyrite; Thin films; Real-time X-ray diffraction

The Impact of COVID-19-Related Measures on the Solar Resource in Areas with High Levels of Air Pollution - Peters, Ian Marius; Brabec, Christoph; Buonassisi, Tonio; Hauch, Jens; Nobre, André M. (Joule, 2020)
Restrictions enacted to reduce the spreading of COVID-19 have resulted in notably clearer skies around the world. In this study, we confirm that reduced levels of air pollution correlate with unusually high levels of clear-sky insolation in Delhi, India. Restrictions here were announced on March 19th, with the nation going into lockdown on March 24th. Comparing insolation data before and after these dates with insolation from previous years (2017 to 2019), we observe an 8.3% ± 1.7% higher irradiance than usual in late March and a 5.9% ± 1.6% higher one in April, while we find no significant differences in values from previous years in February or early March. Using results from a previous study, we calculated the expected increase in insolation based on measured PM2.5 concentration levels. Measurements and calculations agree within confidence intervals, suggesting that reduced pollution levels are a major cause for the observed increase in insolation. A broadly noticed consequence of the restrictions enacted to counter the spreading of COVID-19 was unusually clear skies in many regions of the world. Better air quality has an impact on solar power generation, as fewer pollution particles in the air means that more sunlight will reach solar panels on the ground. In this study, we explore how air pollution in Delhi has developed following the lockdown on March 24th and how this reduction has affected how much sunlight the city received. First, we looked at measured particle concentration levels and noticed that after lockdown, levels dropped to about half of where they had been in previous years. Then, we looked at how much sunlight was received by solar panels. Before lockdown, insolation was similar to previous years. Yet, after lockdown, there was a clear and significant increase. In late March, insolation was up by 8.3% compared with levels in previous years. This is comparable to moving a solar panel from Toronto to Houston. Following restrictions to counter the spread of COVID-19, reports about unusually clear skies appeared in many regions of the world. In this study, we explore how air pollution in Delhi has developed following the lockdown on March 24th and how this reduction has affected how much sunlight the city received. Until early April, pollution levels had dropped to half of their usual levels. The cleaner air allowed more sunlight to pass, increasing insolation by more than 8%.
CRIS-Team Scopus Importer:2020-07-24
Keywords: air pollution; COVID-19; solar energy

The influence of CPC reflectors on the electrical incidence angle modifier of c-Si cells in a PVT hybrid collector - Proell, M.; Karrer, H.; Brabec, Christoph; Hauer, A. (Solar Energy, 2016)
PVT collectors aim for the co-generation of pv electricity and heat. The following concept intents to raise the thermal efficiency by concentrating sunlight with CPC reflectors, in order to access a higher number of solar thermal applications.The work presented here, focuses on the influence of the CPC reflectors on the pv efficiency. Parabolic concentrators in general, and CPC reflectors in particular, cause a non-uniform illumination of the pv cells, which decreases the pv efficiency. Ray tracing calculations of one particular CPC geometry result in a characteristic, angular dependent solar flux distribution in the cell plane.The effect of this flux distribution was measured on a real scale experimental collector on a outdoor solar test stand. The incidence angle modifier (IAM) of the pv efficiency was measured for three different concentrations, as well as for an improved CPC geometry, aiming to homogenize the flux distribution in the cell plane.The experiments showed, that the pv efficiency drops from 15% at STC to between 9% and 11%, depending on the solar concentration factor, which influences the efficiency negatively. The predicted efficiency boost of the improved CPC geometry could not be validated experimentally, as the additional optical losses of the more complex setup were high compared to its improvement effect.In order to understand these results, a theoretical model was built, combining ray tracing, electrical and thermal modeling of the CPC PVT collector. This model enabled to calculate the temperature distribution, as well as the pv efficiency simultaneously, by dividing the pvt absorber into finite elements.
Keywords: Concentrating; CPC; Fluid; Flux distribution; Hybrid; PVT

The influence of defects on the cellular open circuit voltage in CuInGaSe2 thin film solar modules-An illuminated lock-in thermography study - Adams, J.; Vetter, A.; Hoga, F.; Fecher, F.; Theisen, J. P.; Brabec, Christoph; Buerhop-Lutz, C. (Solar Energy Materials and Solar Cells, 2014)
CuInGaSe2 (CIGS) thin film solar modules, despite their high efficiency, may contain three different kinds of macroscopic defects referred to as bulk defects, interface defects and interconnect defects. This occurs due to film's sensitivity to inhomogeneities during the manufacturing process. The result is a decrease of electrical power output from a cell or module. In this paper, we present the influence of macroscopic defects on the electrical behavior of CIGS thin film solar cells. To accomplish this, we investigated the relation between the IR-signal emitted of a defect in a cell (measured using illuminated lock-in thermography ILIT) and the respective open circuit cell voltage (V-oc,V-cell) under low light conditions ( < 100 W/m(2)). Furthermore, we developed a modified masking method of measuring V-oc,V-cell of a single cell within a thin film solar module. (C) 2014 Elsevier B.V. All rights reserved.
Keywords: ILIT; Cell voltage; Open circuit; V-oc; Defect; Lock-in thermography

The influence of gallium on phase transitions during the crystallisation of thin film absorber materials Cu(In,Ga)(S,Se)(2) investigated by in-situ X-ray diffraction - Hölzing, Astrid; Schurr, R.; Jost, S.; Palm, J.; Deseler, Klaus; Wellmann, Peter; Hock, Rainer (Thin Solid Films, 2011)
Chalcopyrite based photovoltaic materials Cu(InxGa1-x)(SySe1-y)(2) (CIGSSe) are substituted in the cation and anion lattice to adopt the semiconductor bandgap to the terrestrial solar spectrum. In-situ X-ray diffraction (XRD) investigations on the crystallisation of thin film absorber materials Cu(In,Ga)(S,Se)(2) while annealing stacked elemental layers (SEL) show phase transitions proceeding during the chalcopyrite synthesis. Thin layers of metals with elemental ratio Cu:In:Ga = 3:2:1 are deposited onto Mo-coated polyimide foil by DC-magnetron sputtering. The metal precursor is covered with S and subsequently Se by thermal evaporation of the elements in chalcogen excess (S + Se)/(Cu + In + Ga) = 23. Investigated chalcogen ratios reach from pure Se to pure S. Crystalline phases formed during the annealing of SEL are qualitatively determined. The results are compared to conclusions drawn from previous experiments on Ga-free CuIn(S,Se)(2) absorbers. The presence of Ga and S influences significantly the time-scale and the temperatures of phase transitions, i.e. the sulfoselenisation of precursor phases Cu-16(In,Ga)(9) and Cu-9(Ga,In)(4) proceeds faster with increasing S and is shifted to higher temperatures as compared to Ga-free Cu11In9/Cu16In9. (C) 2011 Elsevier BM. All rights reserved.
Keywords: Cu(In; Ga)(S; Se)2; Chalcopyrite; Chalcogenisation; Sulfoselenisation; Formation reaction; in-situ XRD

The influence of microstructure on the magnetic properties of WC/Co hardmetals - Topic, Irena; Sockel, Hans-Georg; Wellmann, Peter; Göken, Mathias (Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing, 2006)
The magnetic properties of conventional and ultrafine-grained WC/Co hardmetals have been measured and related to the microstructure. The microstructure was characterised using scanning electron and atomic force microscopy. The WC grain size was found to vary between 1.0-2.5 and 0.1-0.3 mu m for conventional and ultrafine-grained hardmetals, respectively. In conventional WC/Co hardmetals the coercivity increases as the WC grain size decreases. In the ultrafine-grained hardmetals with the WC grain size below 0.5 mu m, the coercivity was found to increase strongly and be one order of magnitude higher than in the conventional hardmetals. The relationship between magnetic properties and microstructure in this work can be extended to smaller grain sizes and ties in well with literature results. The developed relationship can be used as a quick method to estimate the WC grain size by measuring the magnetic coercivity. Furthermore, it was confirmed that the coercivity is not only a function of grain size, but also of cobalt content. All results lead to the conclusion that an increase in WC-Co interface area increases the coercivity values. (c) 2006 Elsevier B.V. All rights reserved.
Keywords: WC/Co hardmetals; Ultrafine-grained (UFG); WC–Co interface area; Coercivity; Magnetic saturation; Magnetic domains

The influence of polymer purification on photovoltaic device performance of a series of indacenodithiophene donor polymers - Ashraf, Raja Shahid; Schroeder, Bob C.; Bronstein, Hugo A.; Huang, Zhenggang; Thomas, Stuart; Kline, R. Joseph; Brabec, Christoph; Rannou, Patrice; Anthopoulos, Thomas D.; Durrant, James R.; Mcculloch, Iain (Advanced Materials, 2013)
A series of low bandgap indacenodithiophene polymers is purified by recycling SEC in order to isolate narrow polydispersity fractions. This additional purification step is found to have a significant beneficial influence on the solar cell performance and the reasons for this performance increase are investigated. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: fractionation; indacenodithiophene; organic photovoltaics; purification

The influence of sorbitol doping on aggregation and electronic properties of PEDOT:PSS: a theoretical study - Friederich, Pascal; Leon, Salvador; Perea, Jose Dario; Roch, Loic M.; Aspuru-Guzik, Alan (Machine Learning: Science and Technology, 2021)
Many organic electronics applications such as organic solar cells or thermoelectric generators rely on PEDOT:PSS as a conductive polymer that is printable and transparent. It was found that doping PEDOT:PSS with sorbitol enhances the conductivity through morphological changes. However, the microscopic mechanism is not well understood. In this work, we combine computational tools with machine learning to investigate changes in morphological and electronic properties of PEDOT:PSS when doped with sorbitol. We find that sorbitol improves the alignment of PEDOT oligomers, leading to a reduction of energy disorder and an increase in electronic couplings between PEDOT chains. The high accuracy (r(2) > 0.9) and speed up of energy level predictions of neural networks compared to density functional theory enables us to analyze HOMO energies of PEDOT oligomers as a function of time. We find a surprisingly low degree of static energy disorder compared to other organic semiconductors. This finding might help to better understand the microscopic origin of the high charge carrier mobility of PEDOT:PSS in general and potentially help to design new conductive polymers.
CRIS-Team WoS Importer:2021-07-02

The Interplay of Contact Layers: How the Electron Transport Layer Influences Interfacial Recombination and Hole Extraction in Perovskite Solar Cells. - Hermes, Ilka M.; Hou, Yi; Bergmann, Victor W.; Brabec, Christoph; Weber, Stefan A.L. (Journal of Physical Chemistry Letters, 2018)
Charge selective contact layers in perovskite solar cells influence the current density-voltage hysteresis, an effect related to ion migration in the perovskite. As such, fullerene-based electron transport layers (ETL) suppress hysteresis by reducing the mobile ion concentration. However, the impact of different ETL on the electronic properties of other constituent device layers remains unclear. In this Kelvin probe force microscopy study, we compared potential distributions of methylammonium lead iodide-based solar cells with two ETL (planar TiO2 and C60-functionalized self-assembled monolayer) with different hysteretic behavior. We found significant changes in the potential distribution of the organic hole transport layer spiroMeOTAD, suggesting the formation of a neutral spiroMeOTAD-iodide interface due to a reaction between iodide with p-doped spiroMeOTAD in the TiO2 cell. Our results show that the ETL affects not only the mobile ion concentration and the recombination at the perovskite/ETL interface but also the resistance and capacitance of the spiroMeOTAD.